the Doctor becomes a hermit crab! I absolutely love this scene, he sticks his hand out the tiny tardis, scoots it across the train tracks, makes it to safety, thinks everything is fine then he starts doing a little celebratory dance which is absolutely adorable:
then things go wrong again immediately because the Tardis falls over due to vibrations from the oncoming train and he has to panic, he throws himself over to the console and pulls a big ol' lever and locks himself into a time machine coffin as an emergency measure. the box becomes a little cute gallifreyan cube in "siege mode". the hermit crab shenanigans and the little dance are what make it for me though, the tardis being that size and still absolutely massive on the inside is the sort of silliness that makes me love Doctor Who.