The Cave Serpent is a large snake-like creature with a short neck. However, it has a thick body with four fin-like flippers and an extremely long tail, indicating that it may be an Elasmosaurus, a type of carnivorous plesiosaur, rather than a giant snake. The depiction of the Cave Serpent in King Kong resembles the 'head on the wrong end' version of the Elasmosaurus, a depiction that was later proven to be false.
When King Kong brought Ann Darrow to his mountain lair, he was suddenly attacked by the cave serpent. Kong set Ann down and struggled with the serpent. The creature wrapped its long body around Kong's neck and attempted to strangle him. Kong pulled the serpent off with all his might and slammed it onto the rocky surface of the cave, snapping its spine and killing it.
- The cave serpent may have inspired the other giant snake-like kaiju that King Kong fought in later films, such as the Giant Sea Serpent from King Kong Escapes and the Giant Boa from the 1976 remake of King Kong.
- In the video game adaptation of the 2005 film, during one level Kong must battle two giant serpent-like monsters in a cave. This level is most likely a tribute to Kong's battle with the cave serpent, as the way Kong kills the serpents is by slamming them onto the ground, the same way he killed the cave serpent.
- The Cave Serpent in the original film is actually a Tanystropheus.