The opening scene of Eraserhead plays almost like an initiation test for what follows – if you can deal with this you're in with a chance, and if you're excited by it then you're in for a treat. A literal description of what unfolds would serve little purpose but to further bemuse newcomers to the film. It involves the floating, worried face of lead character Henry Spencer, an embryonic creature with a long tail, a dark and barren planet and a disfigured man who operates a set of old-fashioned signal box levers, which release the creature from the position it has taken up alongside (or perhaps inside of) Henry and plunge it into a pool of silvery liquid. It will likely make absolutely no sense at all to newcomers to the film, and I was several viewings in before it dawned on me that what I was watching was a symbolic representation of conception and birth. But if feels extraordinary. The sense that we are in a dark but very tangible part of someone's subconscious is electrifying. When a small white hole appears in a dark wall and the camera moves towards it, the feeling that we are about to embark on a strange and disturbing journey is overwhelming.

We emerge into the real world, or at least a skewed approximation of it. Henry Spencer is walking home from work, an everyday activity that is nonetheless tinged with peculiarity. The landscape is bleak and unsettling and the soundtrack dominated by the chug of industrial machinery. Henry walks as if he is constricted by his clothing, taking small but rapid steps, walking up and down mounds of gravel like a curious child. He looks worried. He always looks worried. Henry is not a man who seems remotely comfortable with his world and when you see where he lives it's hardly surprising. His tiny apartment is dominated by an old, brass-ended bed, a small table, and an antique dresser. Almost no natural light enters the room and the uplighters on the wall leave whole parts of it in virtual darkness. In place of pot plants there are piles of bracken and earth, an old record player churns out Fats Waller pipe organ music, and a huge steam-fed radiator hisses and clunks at a distracting volume.

If Henry is not exactly at one with himself or his world he is every bit as uncomfortable with others. On arriving home he is informed by his alluring neighbour, who is named in the credits simply as Beautiful Girl Across the Hall, that a girl named Mary has called to invite him to dinner at her parent's house that evening. Henry stares at her with a mixture of alarm and embarrassment, then, with a insincerely mumbled thank-you, retreats into his apartment. The message suggests that Henry has a girlfriend, which is difficult to imagine without visual aids. In a very neat piece of visual exposition, we gather that they are going through difficult time, suggested when Henry scurries around a drawer full of oddities and retrieves and examines both halves of Mary's torn-in-two photo.

The above textual description may create a sense of the strangeness of Henry's world, but not how genuinely nightmarish or how darkly, unexpectedly beautiful it is. Gorgeously lit and shot by Herbert Cardwell and, when the production ran past its first nine months (it was to take an eventual five years), Frederick Elmes, the imagery is a celebration of the unique exquisiteness of black and white, its noir-like use of light and shadow sitting alongside Lynch's first experiments with pushing light levels down so that images only just register on film, which is later taken close to its limit in Lost Highway.

And then there's the sound. Oh, the sound.

With the (often memorable) dialogue kept to a minimum and the music restricted to the distant strains of Fats Waller and sinister electronic hums and bells, it is the unique ambient sound that provides the film with its most powerful tool for assaulting the collective subconscious of its audience. Henry is never left in silence – whether it be the hissing of steam, the chugging of distant industrial machinery, the mournful wailing of factory hooters, the sparking of faulty electricity, the howling of wind or even the bubbling of a hydrator, Henry's world is never an even remotely comfortable place to be, the soundtrack creating a constant sense of unease that feels directly tapped into our darkest dreams. I've lost count of the number of times that people have said to me, after watching the film, that so much of it seems creepily familiar, that it captures with disturbing accuracy what it feels like to have a nightmare. It is this that makes Eraserhead, even after forty or so viewings (yes, I really have seen it that many times), a still troubling place to visit.

Things really move into nightmare territory when Henry arrives at Mary's house. Assaulted by the sounds of interior plumping, exterior industrial mechanics and the high-pitched squeaks of young suckling puppies, he is humourlessly questioned by Mary's mother regarding his job ("What do you do?" – "Oh, I'm on vacation." – "What did you do?"), is momentarily thrown when Mary suffers a sudden but thankfully short-lived fit, and is introduced to Mary's father Bill, a wide-eyed evangelist for the work of the plumbing industry. He never gets to meet the grandmother, who sits catatonically in the kitchen and whose arms are manipulated by her daughter to toss the salad (at one hostile screening of the film, the sight of her prompted a dismayed female viewer to cry out, "Oh God, not another one!").

But it's at dinner that, even by Henry's standards, things take a bizarre turn. Asked to carve up the smallest chicken Bill has ever set eyes on ("Little damned things, smaller than my fist. But they're new!"), Henry is frozen in mid-movement when the creature begins moving its legs and pumping out blood, prompting a peculiarly orgasmic response from Mary's mother and sending Mary crying from the room. If the film hasn't driven you from the cinema by now, this is the acid test, the point at which you'll either go with Lynch or throw your hands in the air and your towel into the ring. All of this is a prelude to the revelation that Mary has given birth and that Henry is the father. Henry doesn't understand how this can have happened so soon after they slept together, but Mary's mother tells him it's premature. Mary, more ominously, blurts out that "They're not even sure it is a baby!"

If the imagery and sound make the film a consistently unsettling experience, what few viewers (myself included) appreciate on their first viewing, especially those who caught it on its original release without the benefit of subsequent Lynch works as reference material, is how genuinely and deliberately funny some of it is. Now I know that a fair few of those who have only seen the film once will be double-taking at that, but this is a view shared by many who have fondly and repeatedly revisited the film, and fans of Twin Peaks should certainly recognise the telltale signs of Lynch's twisted humour, especially (though not exclusively) how it manifests itself in the dialogue and delivery. Those who have sussed and enjoyed this aspect of the film will no doubt recognise and respond to the following:

Bill's whole introductory rant, which he attempts to continue even as he is being chased from the room by his wife;

The sarcastic twang to Mary's mother's voice when, having been assured by Mary that Henry is very clever at printing, she coldly responds, "Yes, he sounds very clever";

Bill passing a pregnant pause by cheerfully asking "Well Henry, what do you know?" only to have Henry squirm uncomfortably and take the small talk seriously with, "Oh...I don't know much of anything...." as Bill continues to grin maniacally at him;

The superb visual gag that sees Mary lean down and repeatedly shake the bed in which Henry is laying in what appears to be an act of madness, but which proves to have genuine purpose;

Henry's unflustered moment of realisation – "Oh you are sick" – as his baby spontaneously breaks out in alarming facial sores;

Henry looking around him in confusion for Mary following an enquiry from The Beautiful Girl Across the Hall about her whereabouts;

The high-pitched, whining "Nooooo!" that escapes Henry when asked if he minds getting married.

And so on. None of which exactly makes Eraserhead a barrel of laughs, but its does run against the claims of my ex-film lecturer, and a fair few others, that the film is unremittingly bleak. It is dark and it is disturbing, but it is also wonderfully imaginative, artistically breathtaking and, yes, nicely twisted fun.

But is this weird for weird's sake or is there something more complex, more meaningful going on here? Lynch himself has consistently refused to supply his own interpretation, and in the accompanying documentary teasingly claims that no review or article he has read has ever understood the film as he sees it. Of the numerous attempts to analyse the film's for deeper meaning, one in particular tends to reoccur and certainly makes as much sense as any other I've come across, and in Part 3 I'll be attempting to pick this apart.

It should be noted that in doing so I will be discussing the film's final scene and even the ending, so if you're new to the film or have seen it and would like a go at working it out for yourself, you might want to skip straight to the DVD details.