Baleen whales eat plankton and krill. Plankton are clouds of very small fish floating in the water. The whales' mouths are very large. They open their mouths very wide and hold a big mouthful of sea water. Their throats stretch very wide to make the space inside their mouth even bigger. Then they close their mouth and squeeze out the seawater. The food does not escape because, instead of teeth, these whales have filters called "baleen". Baleen is long, hard strips that act like a strainer. The water goes through the baleen. Animals and plants in the water are trapped and swallowed, while the water goes back out. This is very different from the way that toothed whales eat.