Smiley is a dog that lived in an animal pound and was due to be put down.
History
Lisa decided to adopt him to save him, along with several other animals. She hid them all in the attic, where Bart found them.
After a tiger had mistakenly bitten his arm, all the animals had to be taken away. Chief Wiggum told Lisa that her animals would be taken to a pound and killed if she could not find a suitable home for them.
Bart felt empathy for Lisa and decided to use the money, that he raised for the operation he needed to play the drums again, to build a home for all the animals called Lisa Simpson Home for Abandoned Animals.
