Have you ever seen a video of a penguin pushing another penguin into the water? Yes, this is a thing. This happens because a herd of penguins are usually a selfish herd. This means that they will defend only themselves compared to the whole group. In order to see if the ocean water is safe to swim in, they will push another penguin into the water. If they get eaten by a predator the herd will wait but if the pushed penguin survives, all the other penguins will follow trusting that the water is safe.