If the meaning of this song isn't as deep as in other songs by them, then it's about rape. The father of a small girl forces her to sleep with him and that's why he is an animal. Because he can't tell the difference between human and animal (animals sometimes mate with their children as well). Then, when the girl is grown up and is writing herself a letter with his blood...I think it means that she took revenge to ease her pain.
If the meaning of this song isn't as deep as in other songs by them, then it's about rape. The father of a small girl forces her to sleep with him and that's why he is an animal. Because he can't tell the difference between human and animal (animals sometimes mate with their children as well). Then, when the girl is grown up and is writing herself a letter with his blood...I think it means that she took revenge to ease her pain.