Theory:Doctor Who television discontinuity and plot holes/Planet of the Spiders


 * If the spider is on Lupton's back in episode two, why isn't it squashed when he sits in the various vehicles?
 * Presumably it was slightly 'out of phase' with the rest of the universe, meaning it was intangible as well as invisible, i.e. perhaps in a similar way as the Master used to make the Doctor's TARDIS inaccessible to him in 'The Keeper of Traken'.


 * During this epic chase, why doesn't Lupton simply disappear as he does at the climax?
 * He wasn't near enough to the monastry earlier on.


 * This isn't the same sonic screwdriver as in Carnival of Monsters, so why does Clegg associate it with Drashigs?
 * Perhaps it contains some of the same elements, battery etc., salvaged from the earlier model? This is strongly implied by the dialogue spoken during the dungeon door discussion in 'The Day of the Doctor'


 * Given that the events on Metebelis III in this story are supposed to be taking place many centuries after those on Earth are set (As Arak explains the humans living on Metebelis III are the descendants of space-faring humans from Earth over four hundred years ago) wouldn't the Spider's plan to invade the Earth of the twentieth century create a serious paradox, possibly even averting the historical course of events that would lead the colonizing humans (along with their spider stowaways) to travel to Metebelis III in the first place, and hence compromising their own existence?