A hammerhead is a type of shark with an unusually shaped head that looks a bit like a hammer. Instead of a normal, pointy shark head, a hammerhead's head stretches wide on both sides with an eye on each end. This unusual design serves an important function: the wide head is packed with special sensors that help the shark find fish hiding under the sand. The eyes on opposite sides also give the hammerhead excellent vision, letting it scan a huge area as it swims.

There are several species of hammerhead sharks, ranging from about three feet long to over 20 feet. Despite their intimidating appearance, hammerheads rarely bother humans. They prefer hunting fish, rays, and squid in warm ocean waters around the world.

The word hammerhead can also be used as an insult for someone who acts foolish or stubborn. If your friend keeps making the same silly mistake over and over, you might jokingly call them a hammerhead. The term fits anyone being particularly thick-skulled or refusing to listen to reason.