Monkey corpses are what is left after killing a level 8 Karamjan monkey. The player must have started Tai Bwo Wannai Trio quest in order for it to leave its corpse behind. Otherwise they will only receive monkey bones. The monkeys at the Ardougne Zoo drop them as well.
If a player attempts to use a knife on it, they will receive a message saying: "You don't know how to skin a monkey...yet."