The Giant Clam is an animal that tried to eat Sandy. SpongeBob rescued Sandy, but SpongeBob then got stuck in the clam's mouth. Sandy tosses the Giant Clam in the air and it fell to its demise. However, SpongeBob was freed. This happens in the episode Tea at the Treedome.
In Porous Pockets, a giant clam choked on a pearl, in which SpongeBob and Patrick took, used for Volleyball, and sold, which triggered SpongeBob to be very rich, thus angering Patrick.
Giant Clams in real life are the largest Mollusks, so it's understandable that there was a struggle for SpongeBob and Sandy.