When it is played for drama, expect the character to have crossed the Moral Event Horizon twicefold, since this is an unholy combination of Rape Is a Special Kind of Evil and Bad People Abuse Animals. It helps that the animals in question are not anthropomorphized and are usually the more 'comical' ones found in nature (goats, sheep, chickens). We don't normally worry about the animal, because of said unreality and our moral distance from animals.
It works partly because actual bestiality is rare enough to seem less ' real' than other acts considered perverted, similar to the unreality of cartoon violence - yet common enough that it's more plausible (and seen as less gross by observers, it also doesn't have the same repulsive moral implications) than necrophilia. This is almost always played for laughs, rather than titillation. Usually farm animals, since common pets still might be too squicky for some. Imply that they have a sexual interest in animals. Want to mark a character as a sexual deviant, but confronted with the fact that Discredited tropes like Depraved Homosexual, Depraved Bisexual, and Psycho Lesbian are Pet-Peeve Tropes? Not quite up for the moral gravity of tropes like Rape Is a Special Kind of Evil, Villainous Incest, or Pædo Hunt? Simple.
