The initial hint that you're dealing with a very different animal comes in that first sex-ed class. When they show that slide of the interior female, the shock lasts a long time, I can tell you.You know the one, that diagram - anterior view I think it's called - showing the lower lady thorax's contents in all its glory; uterus, tubes, ovaries and all. No disrespect intended, but when a ten year-old boy is faced with this for the first time, it looks positively alien. Like something a cheap sci-fi movie props man cobbled together, the vague likeness of a venus fly-trap.
Not only are there all those odd-looking parts, but they do odd things, too. Eggs shoot out, stuff builds up on uterine walls, hormones rain all over the shop and there's blood everywhere. (Although sex educators are at pains to point out the wonder, mystery and beauty of all this argle-bargle, stressing that periodic blood is different from circulatory blood.)
See, I paid attention.
The first reaction is "OMG, all that's inside you?" drawing inevitable comparisons to one's own alien parts. In our case, they're only mildly other-wordly, being, as they are, more out there. Besides, the penis is a simple hydraulic/plumbing fixture and more or less self-contained. Balls? Best to consider them biological punctuation.
Puberty and sexual maturity change everything, naturally. What at first seemed gooey and intimidating becomes, well, still gooey and intimidating, but in a way that makes a bloke devote his life to lady-parts exploration. Then there's the secret of actual child-bearing, where the complexity multiplies, together with the possible problems.
For instance, an incompetent cervix is a mere inconvenience to a woman; an incompetent penis would devastate a man. Therein the difference between the sexes.
Bottoms Up, Triffids.
