Koba had walked up to some humans and as they were telling him to leave, he started playing stupid to trick them. Making noises and acting silly. He sat down and drank some of their alcohol but spit it out on them while grunting.

Koba then got up and took one of their machine guns and was swinging it around, still playing stupid. Till he cut the act and shot one of them with the gun in the blink of an eye. A sinister look in his eyes when he aims the gun at the other guy who was absolutely frightened.

Koba killed him too and he smirked with a grunt while still holding the gun he took from them. He had just tricked them into thinking that he was stupid so he could catch them oft guard and kill them. He was a very smart ape.