A porpoise is a small marine mammal that looks similar to a dolphin but with some key differences. Porpoises have rounded, blunt snouts (rather than the dolphin's pointed beak) and smaller, spade-shaped teeth. They're typically shy creatures that stay close to shore and swim near the surface, often porpoising by leaping in and out of the water as they swim.

The word porpoise as a verb means to move through water in that characteristic up-and-down motion, breaking the surface repeatedly. You might see a submarine porpoising as it adjusts its depth, or watch dolphins porpoising alongside a boat. The motion looks like a slow-motion roller coaster, with the animal or vessel rising above the water, then dipping back under, then rising again.

Porpoises are highly intelligent animals, like their dolphin cousins, and they use echolocation (making clicking sounds that bounce off objects) to navigate and hunt fish in murky coastal waters. The harbor porpoise, one of the smallest porpoises, grows only about five feet long. Unlike dolphins, which are often playful and curious around humans, porpoises tend to be more reserved and harder to spot in the wild.