“This is the Masticator's ear. You bit it off after pummeling him senseless. Congratulations on beating him. He's one of the toughest NPCs in the game, especially when you don't have any weapons or armor.”
When you deliver the knock-out blow to the Masticator during the boxing match in the Jungle Gym, the ear might be added to your inventory.
Similarly, the Masticator can rip your ear off if he hits you while you have 110 HP or less. This must happen in order for the player to be able to bite off the Masticator's ear. (Roughly 160+ unarmed is also necessary).