Pickle and Peanut season 2 episode 18
Episode title: Pickledog
Pickle wakes up to discover the lower half of his body has been replaced with a dog's body, and while at first freaked out, he eventually comes to enjoy it and starts having a lot of fun doing every dog thing he can imagine with Peanut, until he discovers that the rest of his body is now being occupied by a very familiar other dog.
