Frodo felt something seize him by the ankle, and he fell with a cry. … The others swung round and saw the waters of the lake seething, as if a host of snakes were swimming up from the southern end.
… The dark water boiled, and there was a hideous stench.
They were just in time. Sam and Frodo were only a few steps up, and Gandalf had just begun to climb, when the groping tentacles writhed across the narrow shore and fingered the cliff-wall and doors … Many coiling arms seized the doors on either side, and with a horrible strength, swung them round.