CNN's John Sutter looks at how animals that are related to dinosaurs, such as crocodiles and alligators, make sounds. We know that bigger things tend to make lower pitched sounds, so johnny just kind of pitched the crocodile sounds way down. When you take a sound like this and scale it up to enormous dinoseur size, it gets to the point where it's actually infra sound. So kind of like inferet is too red for us to usually see. Infra sound is so low it can be hard to hear.