At PrimEvil, billed as "Norfolk's premier scare attraction," the ghouls are fake but the screams are real - and so, apparently, is the strategic planning. Park director Ben Francis has a yearly ritual: briefing his new crop of scare actors on the finer points of terrorizing the public. "We always say to the scare actors, you're going to think the boys will be the worst. They are not."

Francis ticks off the demographics on his fingers like a general surveying the battlefield. Teenage boys "scream like banshees, and run in packs." Teenage girls, meanwhile, tend toward a stony unimpressedness: "Do your scare and move on, because they will get nasty." And mixed groups? "There will be an alpha and he'll be wearing a North Face top." The advice: don't waste your time on the alpha. "He will not react to anything … Aim for the weaker one at the back."

This is the workplace induction at PrimEvil, one of many immersive "scream parks" that sprout across the UK in the run-up to Halloween. For about £40 a ticket, groups of all ages spend the night roaming themed attractions - ghouls, chainsaws, satanic cults, a haunted hospital - and being terrorized by actors and special effects. The risks are minimal, but the spikes in heart rate are very real. And for the scare actors, it's apparently cathartic: "It's the best form of therapy and you get paid to do it," Francis says.

Behind the scenes, there's also the occasional "code brown" - the industry term for when a punter's fear gets the better of their digestive system. Because nothing says Halloween like a grown man in a North Face top sprinting from a chainsaw-wielding clown, only to be outdone by the teenager at the back who faints. Happy Halloween, Norfolk.