OK. Intact men and cut men have (generally) different thrusting patterns. I feel like whoever wrote that study doesn't understand the mechanics of penises with foreskins. Quick explanation: Cut men, who have lost the most sensitive part of their penis, usually require harder thrusting than intact men. They pull out farther, they push in deeper. Observations by women familiar with both bear this out. Consider the mechanics of the foreskin, combined with the tendency of intact men to thrust less. A lot of the movement of the intact penis is in and out of the foreskin sleeve. Yes, it's taking place inside the vagina, but there's less friction. Hard to explain unless you have a foreskin or have a regular partner who is intact.

It seems to me that a natural penis would tend to scoop any existing semen right into his own foreskin. There it would mix with his lubrication and then a mixture of his natural lubrication, her natural lubrication and the existing sperm from the previous guy would be circulated inside the vagina with each movement. (You could make a case that this action ENCOURAGES women to have an extra partner, because this would provide a fantastic environment for the sperm! All that mixed up body fluid would nourish the sperm of any partner she might have within a day or so!)

At any rate, the sperm reaches the cervix as soon as 15 minutes after ejaculation, so unless the woman has had sex with two men back-to-back (as it were) it's already too late for Dude No. 2 to do anything about it. (His sperm might well benefit from the presence of the other guy's seminal fluid, though. So if the first guy's sperm didn't impregnate her because he's infertile or she only just ovulated or by pure chance, Dude No. 2 has a better chance.)

This is why douching after sex isn't a good way to prevent conception. If the sperm were just hanging around in there for long periods, we could just douche afterward. Clearly that doesn't work!