Boomerang Pet Ball
The Boomerang Pet Ball is a toy that SpongeBob bought for Gary in the episode Gary Takes a Bath. It made its only appearance in that episode.
Design on the box
It says "New Boomerang Pet Ball Really Works".
What it does
The ball is supposed to "boomerang" off things or in mid-air. The box also boomerangs off things, which then hit SpongeBob in the face.