Marine Animals Do squid have three hearts? And dolphins ears? Do sharks have to swim all the time? Take the test and find out if you know the correct answers. True or False? - Marine Animals Dolphins don’t have ears. Octopuses have three hearts. Killer whales kill people. Chairs are more dangerous than sharks. Dolphins recognize themselves in mirrors. Sharks have to keep swimming to stay alive. See all "True or False?" quizzes!