It's true! Sometimes my siblings will be watching a movie in the room next to this one, and all I can hear is screaming, panting, moaning. I quite often have to peer in and see what porn flick they've rented this time (not that they've a habit of it), only to find out that it's actually some messed up horror movie.

I guess this is most prevalent when they have the running from the big scary monster/person/whatever scenes. Take note:

"AHhhhhh!!! OH GOD!!! *heavy breathing*"
-= some thing tackles the petrified, helpless woman =-
"Get it away from me! Nooo! AHHH!! *gasp* *moan* *pant*", etc.

Granted this might be a pretty sadistic porno, but it accentuates my point I think. The tacky "scary" music they play in some horror films, is also kind of similar to sci-fi porno music. (Not that..I..would..know.. no, really..) Ah, the utter crazyness of the horror genre.