THERE are some films which make you wonder exactly what kind of shenanigans their creators get up to behind closed doors. Such a movie is The Human Centipede, a warped and twisted horror movie which will make even the sternest constitutions waver.

Two airheaded American tourists (Ashley C. Williams and Ashlynn Yennie) are on a road trip in Europe.

Breaking down and getting soaked in the rain, they stumble across the house of Dr Hieter (Dieter Laser) where they seek refuge.

Little do they realise he’s a discredited but brilliant surgeon who once specialised in conjoined twin separation but now has gone utterly insane.

After drugging them, he sets about crippling them, removing their teeth and sewing them and another Japanese man (Akihiro Kitamura) together ass-to-mouth as a three-person chain in a grotesque surgical procedure.

One can’t help but speculate as to how this movie was cast - “Wanted: Actress to spend 90 minutes on camera with her face between an Asian man’s butt cheeks. No experience necessary.”

It’s a premise which is as puzzling as it is shocking.

Other than obvious insanity, it’s never revealed why Hieter wants to sew three human beings together in an organic daisy chain. One can only assume that he’s doing it because he can.

The same can be said for director Tom Six, who presents us with a an intriguing and unnerving surgical idea but one which appears to have little point other than to shock.

Once you get past the revulsion of the surgery, the film quickly lapses into tired horror movie clichés; it’s as if once he’d conceived of the idea, he couldn’t really think of anything to do with it.

That’s not to say it's devoid of interest beyond its depravity.

Neither of the girls can understand Hieter’s German and neither can speak because they have their mouths sewn onto the person in front’s anus.

The man at the centipede’s head doesn’t understand English and only speaks Japanese, which none of the others can comprehend and their lack of communication makes their attempted escape all the more pitiful – a sequence which is almost heartbreakingly tragic, a surprising emotion in a film so perverse.

For all its limitations it’s still a visceral and truly unsettling film.

Six wisely chooses not to show too much gore but let’s the imagination fill in the blanks during the surgical experiments – that which you do not see is always more terrifying than what could possibly be seen on screen and there’s enough suggestion to send your mind down the darkest of alleys.

The wonderfully named Dieter Laser is perfectly cast as Dr Hieter, a mad scientist in the true classic sense.

He could easily be a remnant from the Nazi experiments of the Second World War, alternating between staring bug-eyed and unblinking into the camera one moment and deriding his subjects with foam-flecked impatience the next.

Wearing a lab coat, sunglasses and wielding a rifle, Laser is easily one of the creepiest villains ever to stalk the silver screen.

It’s actually much more restrained than its subject matter would initially suggest but it’s certainly not for the faint hearted and not exactly ideal first date material.

If an apple a day keeps the doctor away, I’m building a tree house in an orchard tomorrow.

The Human Centipede (18) is out tomorrow.