Whales are divided into two groups based on how they catch food: toothed whales must chase and catch individual pieces of food using teeth suited to their needs, while baleen whales strain plankton and krill from water using baleen plates made of keratin like fingernails. Key differences between the groups include toothed whales having a single blowhole and baleen whales having a double blowhole, and examples of whales in each group are given such as killer whales for toothed whales and humpback whales for baleen whales.