According to science, you can trick a monkey, but it’s all in the technique you use. For example, there is a famous magic trick among humans called the French drop, where you show a penny in one hand and pretend to hand it off to the other hand, but actually drop it into the palm of the original hand. People and monkeys with opposable thumbs expect the penny to be in the second hand, but monkeys whose hands don’t move like that aren’t fooled, as they wouldn’t hold a penny with their forefinger and thumb. Researchers modified the trick to a more monkey friendly fist holding the penny, which managed to fool them. It’s all about knowing your audience.