"This is why a rapist does not have to be physically violent, or state in clear terms that he intends physical violence, for forceful rape to occur. When somebody has illustrated that they are willing and able to step so far outside of the boundaries of human safety, a victim has every reason to expect that there are no boundaries on their behavior. If this person is willing to have sex with somebody who very clearly does not want sex, that person is probably also willing to, or at least capable of, causing physical injury when the lack of consent turns to a physical struggle….
A rapist does not have to use violence. Initiating sex without consent already indicates how little the rapist cares about your consent in the act. How far does that lack of concern extend? Is this the kind of rapist that could continue to enjoy sex when their victim is in obvious physical pain? Could they enjoy causing the pain? Is this the kind of rapist that will happily kill their victim afterwards? A victim has no idea, whether the rapist is a stranger, acquaintance, friend, family member, boyfriend, or husband. Because if a victim could look at a person and know that they were capable of rape, they would not be within physical proximity in the first place. A victim doesn’t know their rapist is capable of rape until a rape begins; and once a victim knows that, they have no idea what else their rapist is capable of. A rapist does not have to threaten further violence. The rape is threat enough."

— Harriet J, http://www.fugitivus.net/2009/01/08/another-post-about-rape/