Sense of self
Can you imagine what it would be like if you have never seen a mirror before - to see your reflection for the very first time? In some chimpanzee colonies, researchers have provided mirrors to allow chimps to get up close and personal with themselves. The chimps' first reactions are usually social in nature, so you might see a little bit of aggression as they get used to this new chimp, or sometimes even a little bit of play. Eventually the chimps start to test the relationship between what they are doing and what they are seeing, realising that the other chimp is doing exactly the same thing. These are the first signs that they're understanding it's their movements that are making these reflections happen. They then begin to explore parts of their bodies they have never seen before, inside their mouth and their eyes, looking at their teeth. The reason these chimps are able to do all this, is because they - like us - have a sense of self.