We watch “Cold War” (Series 7, Episode 8) where the Doctor and Clara travel to Peter Davison’s fifth Doctor era (that’s 1983 to you younguns!) and encounter Jon Pertwee’s 3rd Doctor era villain: the Ice Warriors! Whilst said encountering is going on, Matt Smith’s canonical eleventh Doctor tries to warn the scientist portrayed by the prototypical bad guy from nearly every movie made in the past forty years (David Warner…let’s give credit where credit is due) that his South Pole ice cube contains evil! Evil I tell ya! (Grampa Simpson appears in this description courtesy of Disney which I assume owns the BBC and everything else by now.)