One difference between chimpanzees and monkeys
A chimpanzee can learn to recognize itself in a mirror, but monkeys can't.
Mirror facts and facts about mirrors, from the Random Facts shelf.
2 facts on this shelf

A chimpanzee can learn to recognize itself in a mirror, but monkeys can't.
One twin is always born healthier and bigger then the other because of the unbalanced distribution of nutrients during pregnancy. Some identical twins are actual mirror images of each other, e.g. one will be right-handed the other left or one is near sighted the other far sighted etc.