Cats are secretly magical fey creatures who naturally have senses we humans cannot comprehend.
While their physical forms are maintained on a high protein diet, their spiritual forms feed on attention. Their senses are finely tuned from centuries of evolution to know exactly where to prod to milk their humans of the most possible attention.
This is a symbiotic relationship, not a parasitic one, as we humans receive purrs and positive psychic energy from our satisfied cat friends. Plus their demon hunting tendency is a welcome bonus around the house.
Mine mostly goes for the boobs.