As fun as it is to watch folks get dragged by horses or swim in a tank of alligators, even ”Fear Factor” producers admit that what pulls in an average 12.2 million viewers each Monday is the show’s staple gross-out stunt, like the recent cow-brain-eating contest. ”It’s viewers’ favorite part of the show, and it’s the cheapest part, too,” says executive producer Matt Kunitz. ”It doesn’t cost very much to eat a worm.” But it takes a lot of research, which is why former ”Oddville, MTV” host Rich Brown works full time to find the world’s ickiest eats, such as the Madagascar hissing cockroaches (note: It’s best to chew, not gulp down, the two-inch-long insects). But even Brown has his limits — he won’t force contestants to consume human placentas. There are several other disgusting stunts he’s partial to staging, though, like asking players to put a gut-pumping tube up their noses after downing a concoction of Pepto-Bismol, Mountain Dew, ketchup, and milk (to which Kunitz has given a thumbs-down…for now). Sure, such stunts may turn a few stomachs, but Brown is convinced they have appeal. ”Americans are not really experimental when it comes to food, so a lot of this is new and scary to them,” says Brown. ”It’s sort of like we’re horrified yet fascinated at the same time.” Not to mention nauseated.