Fish have a special mouth that helps them eat their food. Their mouths are very different from our mouths. Fish have something called a buccal cavity. They open their mouth very quickly and their buccal cavity creates a suction, like a vacuum. So they suck in their food with all the water that rushes in! Then they let all the water go out of their gill flaps and the fish swallows the prey. So, next time you feed your gold fish, stay and watch. Or check out this slow-motion video to see for yourself. It’s really cool.