Bentley: What's with this industrial-strength voodoo gate? Mz. Ruby must really be trying to keep something out.
Sly: Or maybe... she's trying to keep something in!
― When approaching the gate[src]
Sly stumbled upon a gigantic voodoo gate that Mz. Ruby apparently built to keep something from entering or escaping. Sly climbed up and around the gate, entering into a swamp-filled lair, which happened to be home to a massive sea serpent known as the Beast. As Sly ventured through the swamp, Bentley took note of the moving reeds in the swamp and advised Sly to keep moving. Sly eventually encountered the creature, who awakened and give chase to him through a thicket. Sly barely made it to the treasure key before the Beast retreated back into the swamp.
I had to overcome some personal demons to get the answer to this one. Try 4-4-4.