Cetacea and two (external) limbs that are modified into flippers. Though not as flexible or agile as seals, cetaceans can swim very quickly, with the killer whale able to travel at in short bursts and the fin whale able to cruise at . Dolphins are able to make very tight turns while swimming at high speeds. The hindlimbs of cetaceans are internal, and are thought to be vestigial. Baleen whales have short hairs on their mouth, unlike the toothed whales. Cetaceans have well-developed senses—their eyesight and hearing are adapted for both air and water, and baleen whales have a tactile system
Toothed whale whale is known to prey on numerous other toothed whale species. One example is the false killer whale. To subdue and kill whales, orcas continuously ram them with their heads; this can sometimes kill bowhead whales, or severely injure them. Other times, they corral their prey before striking. They are typically hunted by groups of 10 or fewer killer whales, but they are seldom attacked by an individual. Calves are more commonly taken by killer whales, but adults can be targeted, as well. Groups even attack larger cetaceans such as minke whales, gray whales, and rarely sperm whales or blue