It's interesting how it's sometimes so clear when animals are play fighting. Sometimes my dogs play fight, and it looks like a real fight if you're not really familar with what's going on. But if you know the animal, you often know that if they were really angry at each other, they could take each other apart in a bloody mess. But this never happens with my dogs! they just like to show a lot of teeth and roll around. Which is what these monkeys look like they are doing.