"Hush, Little Baby" is a traditional lullaby featured in "Spookyfish".
After receiving a goldfish from Flo Kimble, Stan Marsh started seeing threatening messages from the goldfish itself. One night, Stan discovers a dead body next to his bed and started screaming, which Sharon responded. Believing that it was Stan was committed the killing, Sharon decided to bury the body in their backyard and tries to calm Stan down with the lullaby.
Hush little baby, don't say a word.
Momma's gonna buy you a mockin' bird
If that mockin' bird don't sing,
Momma's gonna bury it in the backyard.