The hookworm digestive system is very similar to that of a round worm. They both have a mouth, pharynx, intestine, rectum, and anus. Hookworms don't only affect humans, but they also prey on dogs, cats, and other mammals. They enter their host and attach to the tissue inside the organism to suck its blood. The blood's nutrients are absorbed in the hookworm's intestine and the waste is removed by the anus.