No matter how cruel your partner is, she will deny that anything is wrong. Finally, physical abuse is always preceded by verbal abuse. Verbal abuse is hurtful. Especially when it's denied. Verbal abuse is manipulative and controlling.
Verbal abuse is unpredictable.
No matter how intelligent, careful, or perceptive you are, she'll always find a way to hit a blind spot you didn't even know you had. Verbal abuse is the issue in the relationship. In normal relationships, arguments are over concrete things that can be resolved. In a verbally abusive one, there is no specific conflict - the whole point of any argument is to make you suffer. Verbal abuse expresses a double message.