In the lecture, the professor talks about two ways animals may use to maintain group unity. There are two key points. The first key point is using what is called threatening display behavior. Take baboons for example. When two baboons find some fruit and both of them want to eat it, one of the baboons may stare at the fruit and make some threatening noises. After receiving these signals, the other baboon would walk away and give up these fruit without a fight. Thus, the group unity is remained. The second key point is through use of friendly display behavior. Still back to baboon example. If two baboons do get into a physical fight but afterwards, they would get close to each other and even hug each other, which means that they are not angry anymore, they can still be friends. So the unity is maintained again. Therefore, by giving out these two examples, the professor explains two ways to maintain group unity.