"Impossible?! This is Doctor Who, lest we mortals forget. The show where […] the TARDIS only makes that distinctive noise because the Doctor leaves the brakes on (The Time of Angels) but all the others make the same noise (every episode with another TARDIS.) Yeah, okay, that last one was on me - the episode under ran and that whole scene was spun out of nothing to get us over 40 minutes!" - Stephen Moffat, DWM 469