Julius the cat realises he has somehow put on Alice’s underwear at the start of Alice’s Tin Pony, a 1925 Disney film.
He shows his embarrassment by morphing from a cat into a donkey.
1920s cartoons are full of morphing scenes. Here, the hombre mouse’s hat becomes a motorcycle.
I guess the cartoon is called “Tin Pony” because it involves a train and a train was called an “Iron Horse.”
There’s a peg-legged villain and perspective animation, something you might not expect to find in a Disney cartoon this early.