Daniel Day-Lewis, famous for burrowing so deeply into each role that he doesn't answer to his own name during filming, lived and breathed as Bill the Butcher during the making of ''Gangs of New York.'' Jack Nicholson explained at a press conference following the premiere of ''About Schmidt'' in Cannes last May that he found inspiration in Warren Schmidt's impregnable comb-over hairstyle, and that ''the walk always comes very early -- the walk, the heaviness of the man.'' Adrien Brody learned to play Chopin and dropped 30 pounds to authenticate the talent and emaciation of a Polish Jewish musician hiding from the Nazis in ''The Pianist.''
We know these things because reports on the rigorous creative processes of actors and actresses -- especially of the Academy Award-nominated variety -- are treated as letters of recommendation during awards season. But lost in the public fascination with extreme research is the distinction between preparation absorbed organically into a performance (i.e., Nicholson, Brody, Michael Caine becoming a jaded British journalist in ''The Quiet American'') and acting that shows itself as capital-A, I-paint-with-my-toes Acting.
Sometimes the latter is a conscious, confident choice, the kind made by Day-Lewis, and also by Nicolas Cage, who uses Acting to such charming effect in ''Adaptation.'' Bearing this in mind is a good lead-in to an examination of Spider -- an artful, carefully regulated explosion of craft led by Miranda Richardson and that prince of prickly intensity, Ralph Fiennes.
According to prerelease publicity, Fiennes visited patients at a London psychiatric center to understand the world of Dennis ''Spider'' Cleg, a middle-aged schizophrenic who was institutionalized at the age of 10 and is now living in a halfway house in 1980s London. When we first see him, Spider -- nicknamed in childhood by his mother (Richardson) because of his fascination with arachnids' webs and more metaphorical forms of entanglement -- is just off a train, making his halting way to the dingy establishment run by a brusque matron (Lynn Redgrave), not far from where he lived as a boy.
That nearness does the fragile man in: As the adult Spider relives scenes from his youth (whether true, imagined, or a combination is our decision to make), what little grip he has on reality begins to slip away. There's the implication of a murder, along with the suggestion that his father (Gabriel Byrne) did in Spider's mother for a blowsy, mossy-toothed local tart, also played by Richardson in a grand display of cockney-accented lewdness. But while fact and fantasy are unstable commodities, human moldering is a tangible condition that feels like home to the director of ''Crash,'' ''The Fly,'' and ''Naked Lunch.''
And Fiennes is drawn to the mechanics of portraying mental decay like a fly to rot. Mumbling, shuffling, and scribbling cramped hieroglyphics in a grimy notebook are his broadest gestures, and much of the time he hovers tremulously, recalling a version of the boy he once was (played with chilling maturity by newcomer Bradley Hall). Sometimes there's so much going on in Fiennes' busy inertia that it's exhausting to watch him stand still in David Cronenberg's somnambulant, sparsely populated tableaux. As he did in ''Schindler's List'' (when he went fat) or ''The English Patient'' (when he went burned) or ''Red Dragon'' (when he went tattooed), Fiennes' very skin participates in the project -- his fingernails are nicotine-stained the color of tea bags. The performance works; it's a ballet, a concerto of big, big Acting.