The one thing both males and females share in orgasm is the reaction of the muscles of the pelvic floor. They spasm rhythmically, giving you a tremendously good feeling and also triggering some reactions that help ensure impregnation. The spasms in the male's pelvic floor cause a rapid and good feeling thrusting over and above that which set off the orgasm. The male seminal vessels contract also and do so in a vibrating fashion. The contraction forces out the male ejaculate out. The contracting is not a smooth squeeze like you would give a turkey baster's bulb. It's more of a trembling contracting. If the male pushes out a large amount of ejaculate, you may feel this surging. It's about as rapid as someone rolling their Rs in languages like Spanish. Aside from pelvic floor spasms moving the vagina or anus up and down around the invading cock, a woman's internal passages move in rythmic massaging fashion as well. The idea is like a milking machine, but the feeling of being in her when that's going on is so far beyond any barnyard machinery it seems silly to bring it up. All of this is designed to help ensure the survival of our species. But it sure makes doing that vital work a lot of fun.