The Serpent was a giant mechanical sea monster created by Robert the Terrible and the secondary antagonist in The Pirates Who Don't Do Anything: A VeggieTales Movie.
Back in the cave, the cheese curls turn out to be alive - and vicious. Sedgewick is attacked and, in his desperation to escape being eaten by his own favorite food, discovers he can do anything without giving up. When George and Elliot get to the isle, the rocks, which are really large rock-monsters, start to surround them, but then Sedgewick arrives, having now swum across the ocean followed by the cheese curls. The rocks find the curls amusing and start to interact with them.
The pass opens and one of the rock-monsters helps them get through it. Within the hidden bay, they quickly find Robert's fortress, which is apparently unguarded, but the giant serpent attacks their ship. George and Sedgewick are terrified, but Elliot, overcoming his fear, realizes the guardian is actually just a mechanical device; when it "eats him," he is able to shut the machine down from inside and save his friends.