From the very first seconds of The Texas Chainsaw Massacre (1974), where we are exposed to flashed images of decomposing flesh, to the subsequent news report detailing grave-robbing in rural Texas, followed by the oozing red sunspots of the title sequence, and the opening narrative shot of armadillo roadkill, the viewer is transported to a nightmare zone where usual moral parameters are null and void. That's just the first five minutes. The rest of the movie involves a slow, measured descent into the madness of the Sawyer family, and culminates in a final ten minutes of torture and terror, largely round the dinner table. Domestic violence gets extreme.

The premise is simple. A Scooby Doo-esque van of longhairs (Jerry, Kirk, wheelchair bound Franklin, his sister Sally and bare-backed, micro-shorted Pam) goes to investigate the aforementioned graverobbings to see if Grandfather has been affected. He hasn't. On the way home they start to ignore some dire warnings in the astrology magazines that Pam is set on believing. Franklin's horoscope predicts "a difficult and disturbing day" whilst Sally's reveals that "There are moments when we cannot believe what is happening is really true. Pinch yourself and you may find out that it is". Other warnings come from the more traditional horror genre source of a mad old drunk in the cemetery ("Things happen hereabout they'll tell about") and the gas station attendant ("You boys don't wanna go messing round no old house. Those things is dangerous, you're liable to get hurt.") but all are ignored. When the gas station is out of gas, the hapless hippies fill up on barbecue instead and decide to hang out at the old house until the fuel truck arrives to make a delivery. A fatal choice.

They are trespassers, and, since the slaughterhouse down the road upgraded to more humane methods of killing, there are four rightfully resident Sawyers itching to smash their sledgehammers on the skulls of fresh meat. This sequestered clan are truly grotesque - the gibbering Hitchhiker, the half-decayed Grandfather, the slobbering Cook and of course, Leatherface - and they represent that stubborn, isolationist streak in American backwoodsmen who simply like to live the way they live, and don't want to be answerable to anyone. They'll defend their lifestyle to the death, even if it involves decorating neighbouring homes with chicken bones, and despatching nosey strangers, hence the number of abandoned cars discovered by Pam and Kirk as they explore the farmyard.

For a movie that was banned outright for 20 years in the UK, there is remarkably little gore. Almost halfway through the taut 84 minutes run time, all the blood we have really seen has been oozing from the palm of the Hitchhiker. When Kirk runs foul of Leatherface his despatch is famously speedy, two quick blows with a sledgehammer. Pam's demise is more drawn out, but bloodless - Hooper was aiming for a PG rating and was careful not to show the meathook entering her skin. The audience's over-wrought imaginations have to do the work, here and with the deaths of Jerry and Franklin, which both occur offscreen.

The terror resides in the towering figure of Leatherface, otherwise known as Bubba Sawyer, played by 6'4" Icelander Gunnar Hansen. Bubba never speaks, never reveals his motives, just flails his hammer or cranks up his chainsaw, his face hidden behind one of three masks stitched from the skin of previous victims. His menace is evocative through its simplicity; he lacks the complex motivation of Norman Bates or Michael Myers, he simply is what he is, as his final joyous dance with the chainsaw attests.

Sally Hardesty is the sole survivor of his blade, an early Final Girl. Her torture at the hands of each one of the Sawyer family is the movie's only real nod to excess. She appears to be experiencing punishment for some ambiguous travesty (a sibling spat with crippled Franklin? implied sex with Jerry upstairs in the old Franklin house?), as she is first chased through the woods by Leatherface (her long hair gets tangled in thorn bushes and nearly leads to her capture, perhaps her sin is vanity?), then stuffed in a sack by the Cook, shackled to a skeleton-chair by the Hitch-hiker, and finally served up as Grandpa's hors d'oeuvres. For much of this she screams, relentlessly, is covered in blood, and appears to act without much forethought, leaping through an upstairs (and closed) window. In terms of spectatorship, the audience cannot empathise for long with this extreme and unrelenting state. Instead they distance themselves from her demented semi-nakedness, and begin to view her with the killer's impassivity. Her eventual escape is not a represented as a looked-for triumph, far from it. She does not overcome the monster as her Final Sisters would increasingly manage to do in the 1980s and 1990s, but loses her essential self to him. There is only one character dancing with joy in the sunrise at the end of this movie.

Hooper's initial envisioning of the film required plenty of handheld shots, cinema verité style, but he couldn't rent a lightweight enough 35mm camera - hence the decision to shoot in 16mm. The resultant low budget aesthetic - grain, inconsistent colours, a fly-blown feeling to every frame - adds to the backwoods ethos. There is nothing glossy or civilised about this narrative, it all happens on the fringes of the known world, but the tone is emphatically realistic, from the movie poster declaration that it is "inspired by a true story" to the opening title which refers to "one of the most bizarre crimes in the annals of American history" and gives a specific date to events, 18th August 1973. The documentary feel extends the work done by Romero in Night of The Living Dead, and was much copied by subsequent low budget entries to the genre.

Even today, TCM seems brutally realistic, in a way that none of its sequels or imitators have been able to emulate. For the 1986 sequel, Hooper went for a comedy horror feel, playing to all Leatherface's strengths as an icon to rival Freddy Krueger. TCM III also camps it up, with one of the funniest film trailers of all time (the Lady in the Lake one - if anyone can find it online please let me know), and TCM IV:The Next Generation has the unholy pairing of Matthew McConaghey and Renee Zellweger. Yes, really.

The rather pointless 2003 remake is a hollow attempt to introduce the franchise to a new audience. Ignore it - the original is still very much worth seeing. Equally, the 2006 prequel (The Texas Chainsaw Massacre: The Beginning) is a wasted opportunity to add anything to the myth, despite an intriguing opening.