Easter egg

The term Easter egg referred to two distinct concepts, one of which was related to a part of the celebration of the holiday of Easter on Earth, and the other referring to a secret feature on a digital versatile disc.

Traditional meaning
As a part of Easter, many humans exchanged brightly-coloured chicken eggs or egg-shaped candy, typically by hiding them and then encouraging the recipients to find them.

A popular form of confectioner's Easter egg was made of chocolate and wrapped in coloured tin foil. The Tenth Doctor ate part of one of these before giving the remainder to Christina de Souza, concerned sugar might damage his teeth. (TV: Planet of the Dead)

DVD feature
With the advent of digital entertainment, it became possible to hide some portions of a recording. Principally employed on DVDs, Easter eggs were not obvious on casual inspection of the recording's menu. On more careful examination, or through the use of sequences entered into the playback device's remote control, these "bonus features" could be accessed. Often, the content (or even existence) of the Easter egg would be further obscured when the manufacturer deliberately failed to mention the content on the packaging or in the list of contents.

In 2007, an Easter egg featuring the Tenth Doctor was discovered on seventeen different DVD releases, including Falling Star and Breakfast In The Rain in Great Britain, This lead to some interest among Internet users, like Larry Nightingale, due to the message's cryptic nature. It was later discovered that the message was recorded in 1969 and addressed to Sally Sparrow, as part of a temporal paradox caused by the interference of the Weeping Angels. Those particular seventeen DVDs were all the ones Sally owned at that time. Billy Shipton, a video publisher who was transported back to 1969, put the message on the DVDs in such a way that not even the makers of the discs were aware of it.

Unknown to anyone except the Doctor, the Easter egg message was encoded so that if any of the DVDs containing it was brought into the TARDIS, it activated a prerecorded message identifying it as a control disc, good for a single TARDIS journey. Upon inserting the disc into a DVD drive in the TARDIS' control console, the TARDIS dematerialised and returned to 1969. (TV: Blink)

Behind the scenes

 * In the Doctor Who Confidential episode End of an Era, Billie Piper revealed that chocolate Easter eggs plagued the filming of Journey's End. According to her, the cast of the interior TARDIS scene — during which Earth gets towed home — had consumed copious quantities of eggs during filming. As a result, many of the actors were on a sugar rush, and prone to bouts of hyperactivity and giggling.

List of Doctor Who easter eggs
Many classic-series Doctor Who DVD releases contain Easter Egg content, usually accessible by highlighting hidden areas on menu screens or, in a couple of cases, by letting an episode play to the very end.
 * Spearhead from Space - Unused title sequence.
 * The Movie - Jon Pertwee dedication caption.
 * The Tomb of the Cybermen - Clean 1967 title sequence, VidFIRE test scene, 1967 trailer for The Abominable Snowmen (audio only).
 * The Ark in Space - 2 Doctor Who Exhibition Blackpool promos, VT countdown for Part 2.
 * Carnival of Monsters - Clean 1970 title sequence, VT countdown for Episode 2.
 * The Aztecs - BBC Enterprises ident.
 * Resurrection of the Daleks - Clean 1982 title sequence & closing credits, VT countdown for Part 2.
 * The Seeds of Death - Video clip from the Episode 6 commentary recording.
 * The Talons of Weng-Chiang - Clean 1974 title sequence.
 * The Dalek Invasion of Earth - Sid the Slyther title card, Sid's Date.
 * Earthshock - The Real McCoy.
 * The Two Doctors - Clean 1984 title sequence & closing credits.
 * The Curse of Fenric - Continuity, Mark Ayres bonus interview.
 * The Visitation - Continuity.
 * Pyramids of Mars - Continuity.
 * The Green Death - Continuity.
 * The Leisure Hive - Continuity.
 * Ghost Light - Continuity, Outtake.
 * Lost in Time - VT countdown for The Crusade: Episode 3, The Underwater Menace: Episode 3 VHS introduction.
 * Horror of Fang Rock - VT countdown for Part 3.
 * The Mind Robber - Continuity.
 * Revelation of the Daleks - Video clip from the ADR recording for the 5.1 surround sound mix.
 * City of Death - 1979 trailer for The Creature from the Pit, Jagaroth Spaceship advert, Douglas Adams interview, Good Woolf, Bad Woolf, BBC Christmas tape sketch.
 * Inferno - VT countdown for Episode 7, Clean Inferno title sequence.
 * The Hand of Fear - Nationwide.
 * The Mark of the Rani - Continuity.
 * New Beginnings - Destiny of the Doctors outtake, 1981 Lord Mayor's Show.
 * Robot - Continuity.
 * Timelash - Continuity.
 * Arc of Infinity - Coming soon teaser for The Complete Davros Collection.
 * The Time Warrior - The Time Warrior Firsts, Terrance Dicks bonus interview.
 * The Key to Time - Bonus info text, Temporary fault clip.
 * Planet of Evil - Hidden Hinchcliffe.
 * Destiny of the Daleks - VT countdown for all episodes.
 * Beneath the Surface - 1970 trailer for The Ambassadors of Death, Mat's Models.
 * The Five Doctors: 25th Anniversary Edition - Bonus commentary by David Tennant, Phil Collinson & Helen Raynor, 1995 BBC Video ident.
 * Black Orchid - Continuity.
 * The Invasion of Time - Colin Mapson bonus interview.
 * K9 Tales - Larry Grayson's Generation Game.
 * The Brain of Morbius - A letter to Robert Holmes.
 * The War Machines - Location film inserts (mute).
 * The E-Space Trilogy - Mat Irvine bonus interview.
 * Attack of the Cybermen - The Cybernetic Autonomous Dalek.
 * Image of the Fendahl - Louise Jameson bonus interview.
 * The Deadly Assassin - Continuity.
 * The War Games - Location filming audio recording, Scottish Falsetto Sock Puppet Theatre, Time Lord force field film insert.
 * The Black Guardian Trilogy - 3 TARDIS Information Files, Mawdryn Undead: Studio floorplans, VT countdown for all 4 episodes of Terminus, Janet Fielding & Peter Davison bonus interview, Making "The Guardian Trilogy" DVD box set photo gallery.
 * The Twin Dilemma - Film trims (mute).
 * The Keys of Marinus - Patrick Heigham's 8mm behind-the-scenes film.
 * Dalek War - VT countdown for Frontier in Space: Episode 5, plus titles & credits with the "Delaware" theme, Continuity, Planet of the Daleks: Episode 3 (black & white) commentary excerpt.
 * Peladon Tales - BBC News, Location filming audio recording.
 * The Space Museum / The Chase - Enter +++ Enter +++ Zero +++ Stop.
 * Myths and Legends - Scottish Falsetto Sock Puppet Theatre.
 * Kamelion Tales - VT countdown for all 4 episodes of Planet of Fire, Planet of Fire Factoids.
 * The Dominators - Scottish Falsetto Sock Puppet Theatre.
 * Revenge of the Cybermen / Silver Nemesis - 1983 BBC Video ident.
 * Time and the Rani - Regeneration with CGI effects, Eye-Sore, The Name'sh McCoy Shylveshter McCoy.
 * Revisitations 1 - Clean 1974 title sequence, Original un-restored opening scene†, Philip Segal Interview†, Matthew Jacobs' earliest memory of Dr Who.
 * The Seeds of Doom - Outtake, John Challis bonus interview.
 * Meglos - Clean 1980 title sequence & closing credits.
 * Mara Tales - In Conversation: Chris Bailey & Rob Shearman.
 * Revisitations 2 - 1969 trailer for The Seeds of Death (audio only), Video clip from The Seeds of Death: Episode 6 commentary recording, Clean 1970 title sequence, Clean 1982 title sequence & closing credits, VT countdown for Resurrection of the Daleks: Part 2.
 * Mannequin Mania - Unused title sequence.
 * U.N.I.T Files - VT countdown for Invasion of the Dinosaurs: Episode 5, Location filming audio recording from The Android Invasion.
 * Revisitations 3 - Clean 1967 title sequence, CGI sets from The Tomb of the Cybermen.
 * Death to the Daleks - Clean 1973 title sequence & closing credits.
 * The Greatest Show in the Galaxy - The Psychic Circus 1988 music video surviving clip.
 * The Claws of Axos: Special Edition - Reverse Standards Conversion: The Axon Legacy†.
 * The Legacy Collection - Richard Martin's memories of Verity.
 * The Ark in Space: Special Edition - 2 Doctor Who Exhibition Blackpool promos, VT countdown for Part 2.
 * The Aztecs: Special Edition - BBC Enterprises ident.
 * The Visitation: Special Edition - Continuity.
 * Inferno: Special Edition - VT countdown for Episode 7, Clean Inferno title sequence, Being David Burton.
 * The Green Death: Special Edition - Continuity, Global Conspiracy? outtake.
 * Terror of the Zygons - Disney Time, Deleted scene film inserts.

†Was a special feature on the original release.

When the third series of Doctor Who was released to DVD, the Blink Easter egg message was, appropriately enough, included in the set as an Easter egg.