Terry Pratchett once said that there was no such thing as a plot hole, just history being rewritten. That might work for Steven Moffat, who likes to bring out the timey-wimey to excuse continuity errors, but others are still waiting to find out why the Doctor said he was half-human. Every writer has their own take on the show, and every writer adds to the mythology of the Doctor. Sometimes though, writers blatantly ignore what's come before; established facts become blurred when a show runs as long as this one, and given the time travel element, it's sometimes hard to keep track. Here are ten moments in the show though can only be described as plot holes; they oppose the existing facts, they make no sense in relation to what we know, and there's often no kind of explanation for them.
10. Two Hearts Or One?It's an established part of the show these days that the Doctor's got two hearts: he tells us enough, and after meeting Clara, he declared it to be one of the first things that she should know about him. But the binary-vascular system of the Time Lords wasn't established from the very beginning. There's a moment in 'The Edge of Destruction' when Ian Chesterton listens out for the First Doctor's heart, and lo and behold, there's only one beating: did he grow the second one when he regenerated? It's possible that Ian only heard one, but given that everyone who's listened to his heart since has heard two, he couldn't have been checking properly, could he? It's probably a happy accident that the heartbeat of a Time Lord mirrors the drumbeat of the theme tune. There's yet to be a plot when the Doctor's extra heart saves the day, but it's certainly a nice biological detail to the character.