Maybe they are humans?

Did you know – llamas that spend too much time around humans are prone to BERSERK LLAMA SYNDROME. Such llamas believe that humans are fellow llamas, and sneak up behind them to attack.

Adult male inter-llama interaction can be rough, including chest-ramming, charging, leg-wrestling, and biting, and they are strongly territorial. In some severe cases, llamas suffering from BLS may sneak up to their owners and attack them from behind. Male llamas suffering from this condition become dangerous when this behavior is directed toward humans and they usually have to be euthanised. Female llamas can also suffer from berserk llama syndrome but their behavior is usually limited to spitting and difficult handling.