Sharks' relatively large and complex brains are comparable in size to those of supposedly more advanced animals like mammals and birds. Sharks also can be trained. Most sharks prefer to eat certain types of invertebrates, fish and other animals. Some sharks eat mainly fish. Others eat other sharks or marine mammals.
Some sharks are even plankton-eaters.
Most sharks don't appear to be especially interested in the blood of mammals as opposed to fish blood. Sharks eat periodically depending upon their metabolism and the availability of food. Sharks attack their prey in whichever way is most convenient, and they can protrude their jaws to bite prey items in front of their snouts. That's why man must now do all he can to preserve them.