Near the end of the Chicken Island West stage, there is a hidden cave on a cliff wall just above the ocean, specifically just near an outhouse, that can be most easily accessed by hovering down into it with the Chicken Suit. Inside the cave is a shrine with four torches, and in the center a portrait of an "Apedog" (a dog with a chimpanzee's head) with the caption "eatpoo" in lowercase lettering just below it. This is a tribute to a now-defunct online art forum called EATPOO, which one of Avalanche Software's developers frequented at the time, and of which Apedog was the mascot.
Unused audio clips regarding Numa Bay can be found in the PlayStation 2 and GameCube's files. The Game Boy Advance version still includes this stage in the final version.