Sex is not a tap, we're told. Real sensuality is something that flows, right? It's effortless, and you exude it — you either have it or you don't. Therefore, for a woman or an actress, any attempt to be sexy must be the unsexiest thing there is: an act of grim determination, rather than spontaneity. It's not as if you can switch desire on and off.

But what if you could? What if sex was just part of an actor's skill set — and chemistry was something you could control? When actresses visibly turn on sexuality — as opposed to just giving it off — the results can still be highly effective. Sex which is part of someone's repertoire may be all the more mysterious because we know it can be deployed: at will, and with variations. However, few stars do this without cynicism. Sensuality only works when the ego is kept out of it: think of Demi Moore, and her very professional appearance. In other words, an actor is better off playing an actual gold digger: the marketing needs to be in the script rather than behind the scenes.

Flirtation can be one of the most exciting forms of acting, and transformation: it's something that either clicks or doesn't, yet the presence needs to change in an undefinable way. However, the actor's lack of self-interest is key: career can't be the only motivation. Therefore, the following is a list of women who don't bloom unless the plot tells them to. But they can all do it on demand. With just a dip in her intonation, Holland Taylor gives us a glimpse into a world nearly as ideal as Mae West's — somehow, we get an image of life that's sated but serene. She's best known for her appearances on The Practice and The Naked Truth; in the latter, she opened the petals of a flower, and breathed in the entire blossom — a complete, rapturous inhalation. Tamara Tunie shifts the dimensions of all her work: on film (The Devil's Advocate, 1997), but even in soap operas and legal dramas, she twists interestingly beneath a white coat. On NewsRadio, Khandi Alexander vamps it up with a high kick and nothing else. All of these actresses have been cast as vixens, but even respectable ones can occasionally be persuaded to deliver. What I find fascinating is the way "character" actors respond when their character happens to be a bomb: they get down to business and turn it on. Emily Watson, almost determinedly plain in Metroland (1997), arrives in Gosford Park (2001) with a new strut, and a beautiful, languid scene in the bathwater. Then, as "Lena Leonard" in Punch Drunk Love (2002, above), she appears to have re-aligned her eyes for impact: she holds her head so that the blue line across strikes us first. For Bullets Over Broadway (1994), Dianne Wiest made a conscious decision to be attractive: the character's glamour is tactical and organized. Helen Mirren is a master of the slippery, sexual nuance — she can work it even into a film as bleak as Last Orders (2001). In her last few films, Juliette Binoche has become increasingly sly and womanly: the pure blush of the '80s has been replaced by something less passive — a kind of ripe insinuation. Lena Olin makes no secret of whether her charms are affected: that hair toss (The Ninth Gate, 1999) is designed to rope suckers in — it's clearly had a lot of mirror time. Isabelle Huppert is even more brazen: we can see the thought process behind her gaze, as it's being sent out. In Merci pour le Chocolat (2000), Huppert redirects the film's plot just by catching the eye of a stranger through a window.

These are very considered women: they put themselves out when the script calls for it, but are often prepared to be "unexceptional" until then. The genre which lends itself to this kind of attitude is, naturally, the gold-digger comedy: whether romantic, cynical, or screwball, all of these rely on a woman's premeditation. I have to admit, I like practically every gold-digger film ever made: all the Stanwyck ones, of course (from Baby Face, 1933, to The Lady Eve, 1941), but also the ones with a blank-faced heroine (Slightly Dangerous, 1943, Gentlemen Prefer Blondes, 1953), the films where the woman relents (La Baie des Anges, 1963), and even the fun one-upmanship of Intolerable Cruelty 1 (2003). I like those hardscrabble girls, struggling to get by, or maybe just enjoying the climb. For me, any film about a calculating girl seems to drive a little faster, a little more breathlessly — do others feel the same? Directors from Cukor to Chabrol to Hayao Miyazaki have discussed the benefits of using a woman as the motor of a plot. According to Miyazaki, "If a boy is walking with a long stride, I don't think anything particular, but if a girl is walking gallantly, I feel, ‘that's cool.'" 2 Thus, a woman's walk can signal "story" — it's a way of seeming to show objective events, while activating the narrative. Yet having a gold digger creates an added twist. Maybe it's because, finally, there's a reason for the woman to walk the way she does — she can smile or be supplicating, and there's a drive, a curiosity behind it. Ordinary events seem propelled: the film is on its way up. Any kind of behavior is justified. Having an agency gives a woman permission to be sweet, soft, or even, in extreme cases, to be constantly pleasing. In a sense, there's no problem with women smiling all the time: all we want is a pretext.

For me, the best instance of a woman "walking the walk" recently is David Mirkin's Heartbreakers (2001). It is, of course, a film about scam artists, but it's also one of the finest screwballs of the last decade — certainly the dizziest and most exhilarating. It's the kind of film where your mind gets plugged into whatever the schemer is doing: every bit of last-minute ingenuity makes you lunge forward, and the success of the grift spurs you on. Each overhead shot seems to suggest that this is a world for opportunists. A movie that turns on quick thinking is always exciting, but in Heartbreakers the ideas get more and more loopy. This is largely because Sigourney Weaver (as Max) is so silly in it: this actress has a big body tuned into some unknown wavelength, although it's clearly a high one. In order to dodge the plot's various obstacles, Max is "forced" to make several impromptu performances — as a Russian émigré, as a cabaret singer, as a woman with morals, and also as someone who would be comfortable having sex all the time. Of the demands of the role, Weaver said, "If I have to turn myself into someone who's a miniskirted vixen, I can do it because I have no choice. I'm an actor." 3 From anyone else, this would sound like a coy boast — actors are constantly making ridiculous remarks about having "no choice" other than to take part in tasteful nudity. But this isn't the statement of a career professional: taken at face value, it's a rather interesting view of acting range. Maybe it's every actor's responsibility to be able to "do" sexy, and to get there in a matter of minutes. Forget about snazzy technique: they just have to make the mood shift, undeniably. And Weaver can do it: the air snaps with purpose when she tilts her captain's hat on a yacht. A white shirt sends a clean breeze towards us. When she needs to distract a workman, she leans back and it takes only a second for her vibe to become indolent, luxuriant — and self-parodying. For the right performer, seduction is a script challenge: a deliberate tool, but also the act of someone who has no choice but to be uselessly, needlessly suggestive.

For Max, Ann Roth has created the kind of wardrobe that Lana Turner or Joan Crawford might have had in their vacation films of the '40s and '50s. It's a glamorous resort style specific to movies: head-scarves, bodysuits, large hats over linen. As well as her share of demure outfits (a stab at "age-appropriate" dressing), there are black opera clothes, and a stunning, white-gold sheath. All of these are worn specifically as costumes — intrinsic to the film rather than product placement — and thus they are perfect for committing antics. For nearly a third of the film, Weaver plays a Hollywood Russian (a very '40s idea in itself), starting every sentence with "Is" or "Is not," and inventing new ethnic expressions ("Poi, poi!") along the way. In these movie-star get-ups, Weaver brings acting back to the level of paint, artifice, and fake accents. This, then, is the modern actor's task: to be expressive as she passes through different atmospheres — through different nationalities, impromptu renditions of songs, and in that fluid region between comedy and the sublime. In this context, it's a shame Weaver hasn't had the chance to do more farce. Imagine her as the chimp princess in Burton's Planet of the Apes (2001), swinging from branch to branch, arguing the case for humankind. Although Helena Bonham Carter nearly got the humor of it, a huge comic potential was missed in this character: a well-intentioned, hairy but fragile being, self-consciously sympathizing with a "lower" species. And while Catherine Keener was acceptable in Being John Malkovich (1999), how much more exciting would it have been to see Weaver moving through the different phases of Malkovich: amping up the excitement, urging strangers down the chute into the actor's brain?4 New mannerisms could have been created for each floor of the film's building — we would have felt a shift between her 7 and 7½. The idea of a psychic portal was made for her.

In Heartbreakers, it's no surprise that Max is seen getting her training from Anne Bancroft: someone who knows a thing about comic seduction, and who always trotted sex out as a series of signs — voice first, then the outline of the eyes, and then the body. However, Weaver's ability to project either glamour or reason means that we never really take in the strangeness of her face. It's an iconic image we don't know much about, particularly in comedy: because her eyes do a lot of the work, we don't notice how austere her face is, and it's odd that it seems unquestionably attractive. There's a very fine chiseling in the lower half: it doesn't really need to be that fine, for all the attention we pay it. So it can seem like the flat detail of a painting — precisely done, for no reason. Yet when it comes to marrying men for the right reasons, that section comes back into play. At the end of the film, the lines are there to show agility, and a subtle play of feeling and hesitation as she spares her last target. After all, Max is not a caricature: this is a complex, half-hearted gold digger. As in Gentlemen Prefer Blondes, nothing's more moving than an operator who can't close the deal.

Few actresses with such moves would use them either so discerningly or with such wild gestures of total unleashing. On and off-screen, the tendency is for women to naturalize their mystique, as well as their class. Young actresses like Kate Beckinsale and Gwyneth Paltrow hold themselves to attention: for them, poise and "breeding" equate to tightness, a restriction of movement. Being regal looks onerous. No one could be more "born to it" than Weaver, but for her, confidence in style means being free to let go: to hunch into a scene, and make it the schlumpiest hunch ever — no need to signal the fine mind behind it. It means being able to loosen your backbone, waggle that great lofty head, and live out the cliché of letting the emotion of a scene enter you. (Weaver has expressed a desire to work with Jim Carrey, but she's more flexible than even him. Her approach has more follow-through: the fact that she's a looser performer means that the joke doesn't snap back — it never ends.)

Watching Heartbreakers, I'm starting to wonder if anyone has had so much freedom in front of the camera. It's true that Barbara Stanwyck could "do anything," but we never questioned that we were watching the workings of a mind, or even that we were dealing with a human brain. However, in comedy, Weaver seems literally out of it. On Saturday Night Live, and in Ghostbusters (1984) and Galaxy Quest (1999), what we see is a long, unstable body — supposedly a figure of grandeur, with a mop on top — barely holding onto coherence. Words emerge from its mouth with an occasional charge and purpose, but generally with a wooziness that drugs the viewer. It can turn sultry, on impulse, then suddenly set its jaw for a moment's composure, before turning back again. It floats when pushed. Today, only Weaver (like Paula Prentiss before her) reminds us that actresses doing sexuality is like actresses doing comedy: being funny is about seizing that same vibration out of the air. It's there and then it's not.