Foxy by Proxy (1952)
Bugs Bunny: Those dogs may get a fox's tail but they'll never get a rabbit's tail.
[most naive and chubby dog sneaks up with a pair of scissors and snips off Bugs' tail and runs away with it]
Bugs Bunny: Okay, just call me "Stubby".
[then the closing credits start]
[just after Bugs Bunny, in the fox uniform, sets fox tracks next to train tracks, the naive dog grabs Bugs and threatens to cut off the fox tail. But after 'foxxy' Bugs Bunny asks what type of tracks, the dog was following, the naive dog remembers that it was on train tracks and goes inside a train tunnel, then comes out holding on to a side of a train]
Naive chubby dog: I caught a train, I caught a train, all by myself, I did.