They are always grooming

Opossums may appear untidy, yet they take great care of themselves. Opossums aren't the cleanest animals in nature because of their habit of acting and smelling like corpses. Opossums groom themselves when they are not actively looking for food or sleeping.

According to the Washington Department of Fish and Wildlife, possums, like housecats, often and thoroughly groom themselves with their tongue and paws. Opossums lick their paws and wipe their faces in the same manner. Using their claws to comb their fur and remove insects to eat, they groom themselves from head to tail. When caring for their young, female opossums are especially meticulous in keeping their pouches clean. Because they generally lack sweat glands, opossums are thought to use this behavior to stay cool. Additionally, it makes them smell less (when they aren't secreting nasty predator-repellant, that is).