Horror fans must have been geeked for William Friedkin's return to the genre he helped shape with the seminal 1973 devil possession classic The Exorcist. What may have left some of them cold, and inspired the mixed reaction to Bug, was that this time around, the scary bits are not of the corporeal variety, but more psychological. And rarely has psychological breakdown been wrought so intensely as inside this motel room, where two paranoids (Michael Shannon and Ashley Judd) descend into the mouth of their personal madness. Judd in particular is astonishing, both during her more pensive earlier moments, and in the streams of terrifying babble her henpecked mind produces later on. In some of the most mature work of her career, she might have earned consideration for year-end awards had the film been better received and less stigmatized by its genre. Shannon is the indispensable other half of this mutually destructive pair, spittle flying wildly from his raving mouth. They feed off each other in frightening ways. What's really remarkable is the different moods Friedkin hits. For a long stretch, Bug is a melancholy character piece exploring the miseries of blue-collar life, as Judd's bartender steers clear of an abusive ex (Harry Connick Jr.) and mourns a disappeared child. The film's dramatic change in purpose may inspire criticism that it's uneven or ill-conceived, but the beginning necessarily establishes how these characters' problems are grounded in the real world -- and makes their eventual untethering from that world all the more stark. As the tight staging indicates, Bug began its life as a play (with Shannon as its star). But Friedkin uses his camera as a uniquely cinematic tool, immersing his audience in a claustrophobia they could never experience so intimately while sitting at a fixed distance from the stage.