Thresher sharks are some of the “snappiest” fish in the oceans. They have an oversized tail fin that looks like a scythe—and is almost as deadly. A shark “snaps” the fin like someone snapping a towel in a locker room, stunning its prey. And a recent study worked out some of the details on how the shark does it.

Threshers are found around the world. Most stay fairly close to shore, and not very deep. Adults can grow to about 20 feet long.

What really sets them apart is that snapping motion. A shark first winds up a bit like a baseball pitcher. It twists its body in one direction, its tail in the opposite direction. The tail, which is almost as long as the body, is held high. The shark then uncoils, snapping the tail around in a fast, powerful motion. It then takes a minute to relax before grabbing its prey.

Researchers recently studied the spines of 10 thresher sharks that had stranded on shore or been caught by anglers. The sharks ranged from an embryo to an adult 13 feet long.

The scientists did CAT scans on the sharks, revealing the structure of the shark spines and vertebrae. The work showed that the vertebrae in the body are longer and thicker than those close to the tail—a trait that developed as the sharks got older. The interiors of the two types of vertebrae were different as well.

The researchers said the differences may make a thresher more flexible while adding strength to its tail—allowing the sharks to “snap up” their dinner.