I suspect it's the same explanation as morning wood, which I always understood to be the body's response to needing to urinate but having to hold back; I believe there's a valve which closes on erection to prevent urine from getting into the semen before ejaculation. So, to prevent involuntary urination, the body produces an erection (even a semi-rigid one) to cause this valve to close.
I'm not a doctor, though.
i've heard that too bruddah. i believe it's the prostate that controls the valve, too. but i'm not too sure, so don't go around spreading that info.
i know it's off-topic, but kinda on-topic what with spreading bad info. one of my first asst. managers was haitian american, yah? and she had told me that black peoples have to use greasy hair products because they don't produce hair oil on their own. so i was spreading that information around, and peoples would crack up at me...it's not my fault i'm naive :frown1: but when someone of a certain ethnicity says something, you kinda believe, yah? just like if i was all "oh, we hawai'ians refuse to eat duck, it's a cultural thing. in old times, ducks were seen as holy animals" or something to that affect, unless you knew about my culture, you'd believe me, yah? anyway, just a random little anecdote into the naive and over-trusting life of me :biggrin1: