Baleen is a filter-feeding system made of stiff, flexible plates that hang from the upper jaws of certain whales. Instead of teeth, these whales have rows of baleen plates that work like a giant strainer. When a baleen whale takes an enormous gulp of seawater (sometimes hundreds of gallons at once), it closes its mouth and pushes the water back out through the baleen. The baleen traps tiny creatures like krill and small fish while the water flows through, giving the whale its meal.

Baleen is made of keratin, the same protein that forms your fingernails and hair. Each plate has bristly edges that overlap to create an effective filter. Different whale species have different baleen designs: right whales have long, fine baleen for catching tiny prey, while humpback whales have shorter, coarser baleen for capturing larger fish.

The largest animals ever to live on Earth, blue whales, survive entirely on this filtering system, eating up to four tons of krill per day. Before the invention of plastics and steel, people used baleen to make springs, brushes, and even the flexible stays in corsets, which is why baleen whales were sometimes called “whalebone whales,” even though baleen isn't actually bone.