Shrieking eels are carnivorous sea-dwelling creatures that inhabit the waters near Florin.
They produce loud shrieking noises that steadily grow louder when about to feed on their favorite food: human flesh. Buttercup discovers this when she jumps overboard on Vizzini's ship, to escape her kidnappers. The eels circle around her, enjoying the thought of a fresh meal, and move in for the kill. But Fezzik pounds an approaching eel and pulls Buttercup safely back on the ship before the creatures can get a bite.
- The Shrieking eels do not appear in the novel, where instead Vizzini threatens to cut himself and drip blood into the water to attract sharks if Buttercup doesn't swim back, then the sharks will eat her.