The human zoo - Sex and Super Sex
"One of the most common forms of sadism is rape. Perhaps the reason for this is that it is so exclusively an act of the male that it expresses aggressive masculinity better than other types of sadistic activity. (Males can torture females and females can torture males. Males can rape females, but females cannot rape males.) In addition to the total domination and degradation of the female, one of the bizarre satisfactions of rape for the sadist is that the writhings and facial expresssion of pain he produces in the female are somewhat similar to the writhings and facial expressions of a female experiencing an intense orgasm. Furthermore, if he then kills his victim, her immediately limp and passive condition presents a gruesome mimic of post-orgasmic collapse and relaxation"