my kid is really into sharks, so we get shark books from the library and watch documentaries and such. we've learned a lot about them, including how they reproduce. the males have 'claspers' that they use to deposit sperm into females (no word on whether 10% prefer to stick their claspers elsehwhere). they are particularly noticeable on mature white sharks, waving lazily as they swim by. when i go 'ew' my wife knows exactly why.