Planet of the Ood (TV story)

Planet of the Ood was the third episode of series 4 of Doctor Who.

As the title flatly presaged, it featured the return of the Ood and the Doctor's first visit to their homeworld. It was the first time viewers met Ood Sigma and the first time they encountered the later-important phrase, "the DoctorDonna". It also made little to no mention of the "Missing Planets" arc — Donna mentioned the disappearing bees when the Doctor was looking to find what year they were in.

This episode included the first sign that the Tenth Doctor's life was nearing its end, which would become more evident later on. However, the Tenth Doctor's death did not happen until a significant amount of time later, making the sign of his end extremely early. Foreshadowing the Doctor's regeneration would later be used again for the Eleventh Doctor in 2011's The Wedding of River Song, were "the fall of the Eleventh" is first mentioned.

Behind the scenes, it was notable for showcasing the first prolonged usage of counter tenor Mark Chambers on a Doctor Who score. Later more famous for the purely incidental "Vale Decem", heard as the Tenth Doctor regenerated, here he gave voice to the diegetic Ood song, known on the series 4 soundtrack as "Songs of Freedom and Captivity".

Synopsis
The Tenth Doctor takes Donna Noble to her very first alien planet: the Ood Sphere. There, the Doctor encounters the Ood once more, and red-eye strikes again. But what is causing it this time? He and Donna soon learn the horrible secrets kept by Ood Operations, and they discover just what mankind is capable of. Elsewhere, what is the secret Warehouse 15 holds within its walls? The Doctor arrives, and everything will change. The revolution begins.

Plot
In his office, Mr Bartle, watches a new commercial for the Ood, who are being sold as servants to humans. Bartle is impressed with the advert until he notices the price has been cut to 50 credits each. His boss, Klineman Halpen, tells him it is an economic measure to stay ahead of the competition due to declining sales, and orders him to get going trying to catch up. Bartle orders his personal Ood servant, Delta Fifty, to give him the military export figures, figuring that they will be needing to increase their sales to the army, and tells his assistant Solana Mercurio over his wristwatch to get ready for an impending visit from their clients. Delta Fifty returns with the files but has given him the wrong files. When Bartle asks for the correct files, Delta Fifty, his eyes glowing red, states the files are irrelevant. When Bartle turns around to ask why, he is promptly electrocuted to death by Delta Fifty using his translation sphere.

The Tenth Doctor sets the TARDIS to random settings, effectively taking a mystery tour with Donna. After they land, Donna is excited, yet terrified, about landing on an alien planet. The Doctor comforts her by saying that after all his travelling, he still experiences the very same feeling. However, as Donna steps out of the TARDIS, she discovers they have landed on a cold, snowy planet. The Doctor is overjoyed at the sight of finally experiencing real snow. Donna makes several comments about being cold as he continues on about how much he likes the snow.

He then waxes poetic to Donna about her first time visiting a different planet. As he finishes, he sees that Donna has disappeared, having stepped inside to grab a winter parka. They then proceed to stroll along the snowy plains of the planet. As they do so, they are overflown by a large rocket which Donna comments makes the TARDIS look like a piece of junk in comparison. They then proceed to walk in the direction the rocket was heading.

The rocket is that of Klineman Halpen, which lands at the nearby breeding facility of Ood Operations. Halpen is here to cover for Mr Bartle. Halpen, scientist Dr Ryder, and Solana watch a surveillance videotape of the murder. Dr Ryder cannot explain how the translation orb could be used as a weapon. As for the status of Delta Fifty, a guard managed to shoot him as he escaped, and is presumed to be dying out in the elements. While Dr. Ryder also says that he has no idea about the source of Red Eye, Halpen asks his own Ood, Sigma, for a drink. He protests that it is just hair tonic; he started losing his hair due to stress built up over the last five years.

While the Doctor and Donna roam the planet, the Doctor hears an eerie sound Donna can't detect. They find Delta Fifty dying in the snow. Donna seems disgusted by its look. The Doctor tells her the Ood is a "he", not an "it". While the Doctor examines him, Donna keeps the Ood talking, to keep him conscious. The Doctor asks why Delta Fifty has been shot. The Ood merely says "the circle must be broken", before his eyes glow red and he lunges at the Doctor and Donna. He promptly succumbs to his injuries and dies.

As they walk off, the Doctor tells Donna that the Ood are servants to humanity; they normally aren't violent. But it reminds him of the Ood that he and Rose encountered in the sanctuary base on Krop Tor, who were possessed by the Beast. The Doctor and Donna reach the top of the hill and find the Ood Operations base.

Solana meets up with the buyers outside the warehouse and invites them in for a demonstration and drinks. Just then, the Doctor and Donna arrive as last minute clients. By using the psychic paper, Donna convinces her that they represent the Noble Corporation PLC Limited, Intergalactic. As the guests are being ushered inside, they hear an alarm, which Solana claims is a siren signalling the end of a work shift. In reality, the head of security, Commander Kess, has reported another Ood has broken out. His team pursue the Ood and eventually corner him. When he turns to the guards, they realise that it is more than a mere case of Red-Eye: this Ood has turned rabid. Halpen orders Kess to send the Ood to Dr Ryder.

Solana gives out the presentation on the Ood. She shows three different Ood, one with the standard voice, one with a sultry female voice, and one with a "comedy classic" option; when being told that he has dropped something, he answers, "D'oh!"

Afterwards, while the buyers are enjoying the buffet, the Doctor and Donna discover that they are at the Ood Sphere in the year 4126, during the Second Great and Bountiful Human Empire that spans three galaxies. Donna is fascinated that Earth is still populated, despite all the news articles in her time stating the near end of the world, including global warming and the disappearance of bees. Donna then learns that the red dots on the maps are Ood distribution centres. Donna begins to converse with an Ood, asking if there are any free Ood out there. The Ood merely states all Ood are born to serve otherwise they would die. When Donna asks what the Ood did before the humans arrived, he only mentions the circle, but is promptly summoned away by Solana before he can elaborate. The Doctor and Donna decide to sneak away from the buyers and explore Ood Operations themselves.

Halpen, Kess and Dr Ryder take a look at the chained and rabid Ood. The trio are baffled that after two centuries there is a change in them. Ood Sigma is questioned to see if he has seen anything like it, but even he is just as clueless. Dr Ryder suggests they go to Warehouse 15 to find answers. Halpen reluctantly agrees, even though there hasn't been any activity there for 200 years. When asked about what to do with the rabid Ood, Halpen orders security to shoot it and autopsy it.

Meanwhile, the Doctor and Donna observe the Ood being shepherded around. When one Ood falls, it is promptly whipped by Kess and ordered to get up. Donna realises the Ood are slaves, not servants. The Doctor remembers that he couldn't save the Ood on Krop Tor, and regrets that he never gave more thought to investigate why a species would apparently voluntarily give up their freedom. Now that he knows the truth, and figuring he owes them one; the Doctor resolves to liberate the Ood. They then observe Halpen walking across the property with Dr. Ryder and Ood Sigma. Deducing that he's the boss, they decide to stay out of his way.

Halpen, Dr Ryder and Sigma enter Warehouse 15, which houses a large, pulsating brain - "the Ood Brain". Halpen reminisces about his first time to Warehouse 15 when he was six years old, and is still horrified by those memories. Ryder checks the computers and finds no changes in the brain. Halpen is then interrupted by Solana, who has done a background check on the Doctor and Donna, and found out that they are frauds, and that they are now missing. Halpen orders security to search for the Doctor and Donna, but discreetly.

The Doctor and Donna enter a warehouse, finding countless cargo containers. Breaking into one, they see that it contains numerous Ood. Donna states that the Second Great and Bountiful Empire is built on slavery, the Doctor tells her it's not too different from her time, to which Donna says is not true as she doesn't enslave people. The Doctor quips it's the people who make her clothes. Angered, Donna asks the Doctor if he takes humans with him on his travels just to take cheap shots at humanity. Donna asks an Ood why they won't just go free. They reply that they don't understand the concept. When the Doctor mentions the circle, all the Ood, in unison, say that the circle must be broken, so they can sing. Just then, they are spotted by Commander Kess, who raises the alarm, against Halpen's wishes.

While Solana lies to the buyers and tells them it is just a fire drill, the Doctor and Donna run. Donna is captured by guards and locked in a container with several Ood, which have turned red-eye. Kess operates the giant claw in the room and chases the Doctor with it, intending to crush him with it. Solana stops him as Halpen wants the Doctor and Donna alive. The guards unlock the container and free Donna, just before the Ood could reach her. However, the guards forget to re-lock the container, and the Ood exit the container too and promptly kill the guard next to the door. Kess and his men open fire as the surrounding containers open as well, giving the Doctor, Donna and Solana time to escape as bullets ricochet everywhere. After making it out, Solana confirms everyone on Earth either knows of the treatment of the Ood or doesn't ask. The Doctor asks her to help them. Reluctantly, she points them in the direction where they make the Ood turn to slaves. However, she defects again and calls out for the guards to apprehend the two. The Doctor and Donna head off to the area she pointed out. Kess manages to contain the rabid Ood but believes the entire batch is contaminated. Seeing no alternative, Halpen orders Kess to get gas canisters.

By the time the Doctor finds the area, he hears the Ood song getting stronger, though Donna still can't hear it. After they break into the room, they find several Ood in a cage. The Doctor tries to introduce them as "Doctor... Donna". Donna asks the Doctor to let her hear the song. After he is able to open her mind to it, she quickly wants to stop hearing it. It is a very sad song of captivity. He closes her mind to it again; however, she realises that the Doctor can still hear it, which saddens her more.

While Halpen and the team attempt to break into the room, the Doctor enters the cage and discovers that these are "natural" Ood, and carry a hindbrain in their hands instead of a sphere; he explains that it works as their medulla oblongota, the part of the brain that gives a being their personality. To both of their disgust, the Doctor and Donna realise that the corporation is removing the brains and replacing them with translation spheres; it's effectively a lobotomy to remove the Ood's free will. Donna is saddened to realise just how many issues and horrors await also and wants to go home.

Hearing Halpen's men finally break down the door, the Doctor ushers Donna into the cage with the Ood and shuts the door. He loudly boasts that they are too late to lock them up. They are promptly captured and handcuffed to the wall in Halpen’s office. Halpen interrogates them and assumes they are activists from Friends of the Ood. Halpen claims that the Ood welcomed being turned into slaves, and would be nothing without humanity. Donna snaps at Halpen, calling him ignorant; the Ood are peaceful, and only wanted to befriend humanity. Instead, Halpen's company exploits and mutilates the Ood for profit. Impressed with Donna being able to make such a righteous speech, the Doctor congratulates her. The Doctor also learns that Halpen is going to gas the "livestock", which he likens to how humans dealt with foot-and-mouth disease centuries ago.

Meanwhile, the natural Ood appear to have been affected by the Doctor and Donna's visit as they join in a circle; their song starts intensifying. The processed Ood soon begin holding their heads as if they are in pain, except Sigma, who remains unaffected. The Ood suffering the psychic contact from their brethren turn red-eye.

In the room with the buyers, Solana notices the Ood turn into red-eye and urges the buyers to leave. When a drunk and ignorant buyer is killed after foolishly approaching the Ood, the rest quickly oblige, though several are electrocuted in the process, including Solana herself. It is at this moment that the processed Ood begin a revolution. Another group of processed Ood overpower and capture Kess, release the Ood that he's preparing to have gassed, lock Kess in the cage, and leave him to be killed by his own gas. Outside, Halpen and Ryder witness a full-scale revolution in progress, which the humans are losing, due to them being outnumbered by the Ood.

The corporation plans to evacuate and then destroy the building; Halpen decides to leave the Doctor and Donna behind to be killed by the Ood. The Doctor confronts him about a supposed third element that allows the processed Ood to function; he tells Donna that a creature's mind would be at war with itself without a medulla oblongata to regulate thought. Halpen simply tells him it won’t be around for any longer, and leaves the room to make his way to Warehouse 15.

As the Doctor and Donna attempt to break free without any success, three red-eyed Ood enter the room and begin to approach them. The two of them repeatedly tell them, "Doctor, Donna, friends" and "The circle must be broken". The unprocessed Ood hear this through the mild telepathic link the Ood share and suddenly rise up. The red-eyed Ood stop with their translation spheres close to the Doctor’s and Donna’s heads and then revert to their ordinary eyes, and proclaims them friends. They free the Doctor and Donna, who make their way to Warehouse 15 with the help of Ood Sigma, who was told by Halpen to join his people while he still can.

Once inside, the Doctor finds the giant Ood brain. It is the Ood's telepathic centre and the third part of the Ood physiology. Six pylons surround the brain, which has been used to dampen the telepathy between brain and Ood for 200 years, forcing them to be servants. They are interrupted by Halpen, who holds them at gun point. Ryder tells them that he has surrounded the area with land mines to kill the brain; since it is the third link in the Ood way of life, this will kill every Ood in the universe. The Doctor theorises that the brain spent 200 years adapting to the pylons, but Dr Ryder claims responsibility. He reveals himself as a member of Friends of the Ood; knowing that the natural adapting process would take too long, he's spent ten years infiltrating Ood Operations and working his way up the corporate ladder. Once he finally had access to the warehouse, he lowered the barrier to its minimum setting, allowing the oppressed brain to wreak vengeance on those that imprisoned it. In response, Halpen pushes him over the edge, and he is engulfed by the brain.

As Halpen is about to shoot the Doctor and Donna, Sigma steps in and insists he take another drink. Halpen, disturbed by Sigma's insistence, asks the Ood if he has poisoned him, but Sigma denies such, declaring that natural Ood do not kill. He reveals that Halpen's "hair tonic" is in fact Ood graft suspended in a biological compound. The Doctor realises that the Ood subconscious is divided into three groups: red-eye is revenge, rabid is anger, and the seemingly unaffected Sigma represents its patience. The Ood have been preparing for Halpen for a long time, and with him in such close proximity to the brain, he begins to hear the Ood's telepathic song. By consuming the Ood graft, he has been rewriting his biology. Dropping his gun, he bends down and peels away his human skin from his head, revealing the cranium of an Ood. The slimy, skin-coloured tentacles of an Ood come out his mouth, while Donna looks on in horror. When Halpen stands up, he has been fully transformed before their eyes, then sneezes out his new hind brain, and showing it to the amazed Doctor and Donna. Sigma states "He has become Ood-kind, and we will take care of him".

Donna notes that after being with the Doctor, she doesn't know what is right or wrong anymore, to which the Doctor replies it is better that way. The Doctor deactivates the mines and ask for permission from Ood Sigma to deactivate the pylons, which is granted. The Doctor deactivates the pylons, breaking the circle and allowing the Ood to sing freely for the first time in over 200 years. Outside, the rebelling Ood cease fighting and begin singing. The guards stand down and watch as the Ood group up and sing in unison.

Afterwards, the Doctor and Donna are outside the TARDIS and explain to Sigma that the song resonated to the three galaxies. The humans, realising that the Ood can think and feel like them and demonstrating the immense kindness they are capable of, decide to free the Ood and send them back home. After Sigma thanks them, he offers them a place in their song, but the Doctor says he has his own song. Sigma tells him his song will end soon since every song must end. The Doctor turns to Donna to see what she wants; after the freeing of the Ood, she has changed her mind and wants to continue her travels with him. Before they leave, Sigma tells them they will never be forgotten; their children and children's children will sing of the DoctorDonna. Their names will be carried by the Ood Sphere's wind, ice and snow forever. The TARDIS vanishes as the Ood watch.

Cast

 * The Doctor - David Tennant
 * Donna Noble - Catherine Tate
 * Mr Halpen - Tim McInnerny
 * Solana Mercurio - Ayesha Dharker
 * Dr Ryder - Adrian Rawlins
 * Commander Kess - Roger Griffiths
 * Mr Bartle - Paul Clayton
 * Ood Sigma - Paul Kasey
 * Rep - Tariq Jordan
 * Voice of the Ood - Silas Carson

Uncredited cast

 * Ood - Ruari Mears, Jon Davey, Scott Baker, Ian Hilditch, Iestyn Bryn Jones, Claudio Laurini, Joe White, Sean Saye, Matthew Doman, Kevin Hudson, Jeremy Harvey David Stock, Peter Symonds (TCH 58)
 * Guards - Dennis Gregory, Richard Harris, Mike Freeman, Carl Watson, Andrew Mitchell, Geraint Jones, Eddy Martin, Gerard Morgan, Marcus Hobbs, Nigel Hobbs, Jason Ingram Luke Postians
 * Sales Reps - Tony Gibbons, John Walker, Mark Cunningham, Ian Cunningham, Kwabena Amponsa, Thomas Oxenham, David Ulett, Shelby Williams, David Cordingley, Emma Rogers, Jayne Lutwyche, Kenesha Brown, Helen Roberts
 * Natural Ood - Ruari Mears, Claudio Laurini, Richard Tunesi, Adam Sweet, Kevin Hudson, Jon Davey, Sean Saye, Peter Symonds, Matthew Doman, Scott Baker, Jeremy Harvey (TCH 58)
 * Natural Ood - Ruari Mears, Claudio Laurini, Richard Tunesi, Adam Sweet, Kevin Hudson, Jon Davey, Sean Saye, Peter Symonds, Matthew Doman, Scott Baker, Jeremy Harvey (TCH 58)

Worldbuilding

 * Donna likens a Persil ball to an Ood translation sphere.
 * The Second Great and Bountiful Human Empire is mentioned.
 * The Ood's song is telepathic, and once the circle was broken, all the Ood could sing.
 * A member of Friends of the Ood appears.
 * Donna mentions (for the second time) bees disappearing from Earth.
 * When the Doctor asks Donna where she learnt to whistle, she replies, "West Ham, every Saturday".
 * Solana uses a vidfone to contact visitors.
 * The Doctor claims he and Donna are from Noble Corporation.

Influences

 * The Ood's feral state was inspired by 28 Days Later.

Story notes

 * The snow scenes were shot in a boiling hot week in August, using fake snow. This was done using tiny pieces of paper, as explained in the Confidential for this episode.
 * The transformation of Halpen into an Ood was originally far more graphic, but after the footage was viewed it was re-edited to be less horrific for a family audience.
 * This was the first Doctor Who episode to be produced by a woman since Mission to the Unknown in 1965.
 * Russell T Davies noted during the production of the Ood's introductory episodes that he considered their homeworld to be close to that of the Sensorites — hence the mention of the Sense-Sphere.
 * This episode doesn't show or feature Earth at all, but it is mentioned by Donna and Solana.
 * This episode was originally intended to be episode 2, but was swapped with The Fires of Pompeii.
 * The theme of humans exploiting alien life had previously been touched upon in two Season 2 episodes of Torchwood that aired a few months before this episode: Meat and Reset. The difference here is that freedom for the aliens in the Torchwood episodes came through their deaths, whereas most of the Ood survive.
 * In the episode commentary, it was mentioned that it had been decided to have Dr. Ryder killed by Mr. Halpen as there needed to be good enough reason for the audience to believe Haplen deserved to be turned into an Ood.
 * Adrian Rawlins did the scene himself where he fell over the rail in one take.
 * Ida Scott was going to be a main character in this episode. She would now be a member of an investigative team looking into conditions on the Ood-Sphere, who would be dismayed to discover that her estranged father is now involved with Ood Operations - although it would later be revealed that he is secretly acting on behalf of the Ood.
 * Russell T Davies contemplated devoting a two-part slot to an Ood adventure, but ultimately decided that the storyline would work better if it was not overcomplicated.
 * An extended sequence set in caves beneath the planet's surface, in which the Doctor searches for the giant Ood brain was cut for time.
 * The scene of Halpen, Solana and Dr. Ryder watching the video of Mr. Bartle's death was originally longer, showing Halpen frustrated about having to run Bartle's sales drive. Then he rewinds to watch footage of Bartle calling him an idiot, and decides to terminate the life insurance payouts to Bartle's family as a response to this.
 * There was originally an earlier interaction between the Doctor and Halpen, in which Halpen makes a guest appearance at the Ood demonstration. The Doctor begins asking Halpen questions about the death of Delta Fifty. Halpen tries to make up a story about Delta Fifty being killed by pirates who sell Ood on the black market, but the Doctor doesn't buy it, and Halpen suspects the Doctor is a member of Friends of the Ood. After leaving, Halpen orders Solana to do a background check on the Doctor (explaining why exactly the Doctor and Donna's cover gets blown). The scene being removed also left the proper Friends of the Ood introductory reference out, leaving it as a throwaway mention.
 * One scene would have had the Doctor pointing out that people could use robots just as well as Ood, with two technicians pointing out how cheap and effective robots had become.
 * Russell T Davies wanted to set the episode on an ice world, because this was an environment which had not yet been attempted in the revival.
 * Hoping to explore the underlying motivation for the Ood's eagerness to please, Russell T Davies developed a story that would reflect upon the reliance which modern Western society placed on overseas sweat shops and battery farms, and the wilful obliviousness which underpinned consumerism.
 * At this point, this was intended to be the second episode of season four. It was ultimately decided to be too dark and grim for the slot, so it was swapped with The Fires of Pompeii.
 * Russell T Davies had previously worked with Keith Temple on Children's Ward.
 * In 2006, Keith Temple sent Russell T Davies his script for the forthcoming telefilm Angel Cake, on the strength of which he was invited to a meeting with the production team during the summer. Some thought had been given to assigning Temple a story for season three, although this did not come to pass.
 * Keith Temple imagined Halpen shedding hair constantly, and ultimately swaddling himself in bandages and dark sunglasses.
 * The episode formed the second production block of season four along with The Unicorn and the Wasp.
 * Tariq Jordan's sister Yasmin Paige played Maria Jackson on The Sarah Jane Adventures.
 * Tim McInnerny wore a prosthetic mask with two layers for his transformation scene though the production team's best boy, Peter Chester, provided motion capture for the computer-generated profile of the appendages coming out of his mouth when this needed to be refilmed and McInnerny was unavailable.
 * Tim McInnerny had previously been a candidate to play the Eighth Doctor.
 * Keith Temple's original draft was much darker and more in-step with the storytelling style of the Classic Series, with Temple describing it as a six-part serial compressed into a 45-minute timeslot.
 * Keith Temple and Russell T Davies thought that the episode was not a "fun reappearance" of an old monster; instead, they felt that there was "an actual story to tell".
 * Keith Temple emphasised in his script that the Doctor overlooked the Ood under the shadow of the Devil, and the character had to see his shortcomings.
 * The script emphasised the Ood's slavery; both Keith Temple and David Tennant commented that the existence of a species born to serve was complicated, the latter stating complications with Richard Dawkins' selfish gene theory.
 * Susie Liggat cited the writing as part of the show 's importance—she thought the story about "liberating oppressed people" could be applied domestically or globally.
 * Russell T Davies considered Halpen to be a perfect villain, "a middle manager who's out of his depth". Keith Temple described him as "narcissistic", "preening" and "ruthless ... without sentiment".
 * Tim McInnerny said "It's always nice to play a bastard... I'm glad Halpen's a three-dimensional bastard! That makes him interesting!".
 * Keith Temple epitomised Halpen in a scene where he kills Dr. Ryder; Russell T Davies and David Tennant felt that his "disgusting" and "gothic...Edgar Allan Poe" fate would be undeserved otherwise.

Ratings

 * 7.50 million viewers (UK final)

Myths and rumours

 * This is set before The Impossible Planet. (Most fans assume this because the pre-publicity stated that we would find out why the Ood were slaves, and the date for that story was 43K2.1. However, we never found out what those numbers meant, and there is no reason that this cannot be after that story.)
 * A snippet of the separation music from Doomsday can be heard after the Ood tells the Doctor, "Your song will end soon." He also said that "every song must end." This led to speculation that this was a reference to Rose Tyler's return, and/or an imminent regeneration for the Doctor.

Studio

 * Upper Boat Studios, Trefforest

Location

 * Trefil Quarry, Gwent
 * Twin Peaks Hangar, Barry
 * Aberthaw Cement Works, Barry
 * Hynix Building, Newport
 * Johnsey Estates, Pontypool
 * Hensol Castle, Hensol

Production errors

 * Soon after the Doctor and Donna are blasted backward, fake snow is flung onto the visible screen and sticks in place, which clearly indicates the presence of an outdoor camera that has been used to film the sequence.
 * When Halpen pours the hair tonic onto the Ood Brain, the glass was empty, but when he says he is finished here, it is now full. However, Ood Sigma might have refilled it for him.
 * When Delta Fifty Ood dies, the actor can be clearly seen taking a large breath when Donna approaches him.
 * As the Doctor and Donna are examining the wounded Delta Fifty Ood, the wide shots show his chest covered in snow, whilst the close shots feature much less snow.

Continuity

 * The Doctor sets the TARDIS controls to random. (TV: The Armageddon Factor et al.)
 * The Doctor refers to being unable to save the Ood during his previous encounter with them. (TV: The Impossible Planet, The Satan Pit)
 * The Doctor comments that he visited the Sense-Sphere "ages ago". (TV: The Sensorites)
 * Ryder remarks how he is a "friend of the Ood". Scooti Manista once thought the Doctor and Rose Tyler were friends of the Ood. (TV: The Impossible Planet)
 * also used a massive brain on one occasion. (TV: Time and the Rani)
 * When the Doctor and Donna exit the TARDIS and see the Ood Sphere for the first time, the Doctor comments that he is glad to see real snow. He had encountered "fake" snow three times recently prior to this:
 * Snow that was actually ash from the Sycorax ship breaking up in the atmosphere after it was destroyed; (TV: The Christmas Invasion)
 * Snow that the Doctor had created by using the TARDIS to influence the Earth's atmosphere; (TV: The Runaway Bride)
 * Snow that was really from the ballast from the Titanic after it flew over London. (TV: Voyage of the Damned)
 * Halpen calls Donna "ginger" because of her red hair. The newly regenerated Tenth Doctor was disappointed that he was not ginger, (TV: The Christmas Invasion) as the Eleventh Doctor would later be as well. (TV: The End of Time)
 * Ood Sigma tells the Doctor that his song will soon be ending, a prophecy whose meaning is revealed at the time of the Tenth Doctor's regeneration. (TV: The End of Time)
 * The Ood saying "Doctor, Donna" is not them referring to the Doctor and Donna at the same time, but foreshadowing Donna's destiny. (TV: Journey's End)

Home video releases

 * This story was released in the Series 4 DVD box set in November 2008 along with the rest of the series.
 * It was released as Series 4 Volume 1 in a vanilla edition with Partners in Crime and The Fires of Pompeii.
 * The BBFC has rated this story a 12 certificate citing a "moderate gory scene" presumably referring to the scene where Halpen transforms into an Ood. Partners in Crime and The Fires of Pompeii were both given PG certificates.
 * This episode is the focus of the Series 4 Volume 1 cover.