Somehow, trailer makers can make even the gloomiest comedy look funny or the lamest horror movie look scary, even when the filmmakers themselves can't seem to pull off that trick. It's all done through the magic of editing, and preview editors play by their own rules. In the context of a 2 1/2-minute trailer, Hanging Up looks like a comedy, Three Kings looks like an action picture, and Battlefield Earth looks like a good movie (well, almost). Sure, they're confined to using the existing footage (or at least the footage that exists before the filmmaker completes his final cut of the film), but a particularly savvy editor can create an entirely new movie simply by placing scenes out of context, adding narration, and setting everything to a catchy piece of music.

In the following demo preview, I intend to show how easy it can be to cut a preview for Alfred Hitchcock's Psycho that makes the edgy thriller look like an upbeat romantic comedy. Keep in mind, that I am employing the same tricks real trailer editors use, some outrageously obvious and others more subtly insidious, to pull off the deception. As my model, I've selected Miramax's late-fall preview for Bounce, a generic boy-meets-girl approach that seems to surface frequently enough for films of this kind. Notice how virtually every transition in the Bounce preview uses either a dissolve or a horizontal wipe to join the two clips.

Picking the right piece of music for a trailer is absolutely essential and often serves as the first step in assembling the preview. Music sets both the rhythm and tone by which the editor can work. In most cases, a new movie's score won't be completed until long after the trailer is ready (though some composers, including John Williams and Hans Zimmer, also score the trailers for their films), so trailer editors are free to choose any movie score they please (usually limited to the studio for whom they are working since rights are cheapest and more flexible that way). Editors want their trailers to suggest some sort of recognizable feeling, so they often try to pick a piece of music that evokes that desired emotional feeling.

"Nobody ever sat and watched a movie without music," says Kaleidoscope president Andrew Kuehn. "Even silent film had music. It's extremely important, and it's especially important to us because we're going to put stuff out of context. We're not going to cut things together the way they cut together in the film, and the way in which you can properly make the emotional accommodation for that is with music. It's a very, very powerful ingredient. You may see scenes of films go by for some period of time without a score, but you'll never see a trailer without a score. It's critical."

Though the Psycho preview opens with a coy wink to Bernard Herrmann's violin score and Saul Bass's title design, within moments the music trickles away into Hans Zimmer's whimsical score from As Good As It Gets, a perfect melody by which to introduce Marion and Norman's characters. The music helps rechannel the actual tension of these scenes into creating the illusion of loneliness for the two "lovers."

Through clever editing (though "tricky" would probably be a more appropriate word), we can actually create entirely new scenes. In the film, Marion Crane returns from lunch and offhandedly asks her perky coworker (played by Patricia Hitchcock, the director's daughter) whether she missed anything while she was out. If the new sequence plays as intended, audiences will read it as though Marion anxiously sits by the phone waiting for someone to call while her boss pitifully empathizes with her disappointment. After adding narration, it's not so obvious that Marion's nail-biting behavior in the car results from her suffering from a terrible headache while also managing the guilt of having stolen $50,000 from work earlier that day.

The As Good As It Gets theme repeats as the narrator introduces Norman Bates. In the context of the movie, Norman's shy, aw-shucks mannerisms actually come from a key scene in which Norman retreats to the kitchen rather than going upstairs to face his mother. Working with the AVID (the same editing software used by the trailer industry, though you can actually do the same things with Apple's Final Cut Pro software these days), I have access to a number of discreet special effects, including the "flop" feature that allows me to reverse a clip in which Marion rises from left to right to look as though she is standing up to face Norman ("Two lonely strangers. Two separate lives."). In reinterpreting the available footage, it helps that Hitchcock wants to surprise the audience and lets Norman's peculiar behavior mask his true homicidal tendencies. As the preview presents the scenario, Norman's awkwardness should start to look more like flirting.

Watch carefully in the clip in which Norman explains, "Nobody ever stops here anymore." The sound bite sounds a little rough because I lifted it from another line of dialogue altogether. In a reverse shot that shows Marion reacting to Norman speaking, the lips move similarly enough to get away with it. Previews frequently use this trick, jostling around dialogue while showing the backs of characters who aren't really talking; check out the Dude, Where's My Car? trailer for an example. Here, the trick allows us to give a new meaning to Marion's nervous smile (she's worried that he might catch her signing the ledger with a false name), suggesting that Norman succeeds in charming her with his small talk.

Until this point, the editing has merely been condensed, trying to fit as much footage as possible within a limited amount of space (consider how quickly we must convey the information that a rainstorm appears out of nowhere, Marion spies the Bates Motel in the distance, and she turns off to stop for the night). However, as Marion thanks Norman for his hospitality and he replies by asking her to join him for dinner, I actively accelerate the pacing, lifting out moments of hesitation in the scene to create a very different meaning altogether. Rather than politely deferring to Norman's request, Marion sounds almost excited by the prospect. Percy Faith's Theme to A Summer's Place, one of the most recognizable romantic themes in the movies, seals the deal and provides the backbone for the romantic montage that follows.

In a classical Hollywood montage, an editor uses a piece of music to string together a series of related events. Think of the "Eye of the Tiger" training sequence from Rocky or the scene in The Naked Gun in which Leslie Nielsen and Priscilla Presley fall in love to the sound of Herman's Hermits' "(Something Tells Me I'm Into) Something Good." Audiences seem to turn their minds off to a certain degree during these sequences, a factor I hope won't give away the fact that, say, the two man we see in bed with Marion isn't Norman Bates at all.

I've also tried to have some fun with the narration, recorded by Dr. William Livingston, who provides the voice of "Tex" on the University of Texas's automated phone system. He and I worked together on properly wording the "shower" pun to acknowledge what everyone knows about the movie Psycho without actually letting the preview reveal the movie's sick twist. Since Alfred Hitchcock's name might as well be the trademark on the thriller genre, I chose to emphasize the titles of two of his films that most closely resemble the type of film trailer wants Psycho to be (a melodrama and a domestic screwball comedy): "From the director of The Pleasure Garden and Mr. & Mrs. Smith comes a romantic comedy for anyone who's ever been crazy love."

Whether this approach could possibly sell the movie, much less dupe audiences into thinking that Hitchcock was trying something different with Psycho, is of little consequence. Hopefully, what the exercise will prove is how a devious editor can create whatever he pleases from the available materials and flexible rules of trailer editing. Incidentally, the trailer Hitchcock actually used for Psycho intentionally misrepresents the movie, with Hitchcock walking audiences through the Bates Motel and adjoining mansion while cheerily dropping sly remarks about the locations' curious goings-on, the horrors of which only the film could reveal.