My pet wants a pet

Once there was a boy who wanted something to take care of. Something of his very own. He begged his mother for a puppy. Until she said YES! The boy loved his puppy. He fed him and played with him and cuddled him. But soon, the dog wanted something to take care of something of his very own. So the dog gets a pet cat; then the cat gets a pet bird; the bird gets a pet worm; the worm gets a pet flea.