送交者: Enlighten 于 2005-1-17, 00:41:39:
回答: You mean the contraction of the female vagina? 由 hehe 于 2005-1-16, 23:43:19:
I saw a filmed orgasm (scientific tape), in which the cervix dips into the pool of semen formed at the inner end of the vagina. It apparently increases the chance for conception.
As for the rule, I think the general rule of evolution applies here too, i.e., whatever makes you happy is usually also good for your survival.