What's bewitching and dangerous about the comedian Sarah Silverman is that she can turn a joke inside out until it's no longer clear where the punch line is or, for that matter, where the joke even began.
This is what gave her notorious bit in ''The Aristocrats" -- she reclines on a couch and claims an aging TV host raped her -- such a whiff of voodoo. She played it straight, and it was disturbing.
Silverman turns 35 next month, but to pull this material off, she performs like a pampered teen who's entertaining her friends at the mall food court.
In her new film, ''Sarah Silverman: Jesus Is Magic," when she says, ''I don't care if you think I'm a racist, I just want you to think I'm thin," she sounds both narcissistic and aloof, self-absorbed and oblivious.
The same goes for the movie, too -- often hilariously, sometimes not.
''Jesus Is Magic" consists of Silverman's stand-up act, an arbitrary collection of nasty thoughts about everything from her boyfriend to racism, anti-Semitism, and homophobia. The most uproarious of her remarks can't be reprinted in a family newspaper, but in her universe, those isms have a surreal and curiously piquant everydayness.
Silverman's abrasive material is funny because her approach is friendly. She encourages her niece to be competitive in life: ''Every time you lose at tag an angel gets AIDS," she enthuses. She's an even more upbeat racist: ''And by J.A.P.," she says, ''I mean Japanese."
The anecdote to which that line is attached and other of her observations are interrupted by a handful of skits and sketches. The interludes are nonsense filler that stretch the movie beyond the one-hour mark and leave us underwhelmed by the talent of Silverman's director, Liam Lynch. But they do feature her comedian friends, such as Bob Odenkirk and Brian Posehn.
A few of the interruptions are done as music-video numbers in which Silverman tries to carry a tune in different genres. In one, she shows up at a nursing home to perform a folky song whose most memorable line is ''You're gonna die soon."
This packaged material frequently threatens to cancel out the strength of her live routine because it's self-indulgent, which would be tolerable if it were funny, too. The juxtaposition between that canned stuff and what she's up to on stage offers Silverman in more than one mode, and ''Jesus Is Magic" often feels like the comedian throwing her selves at the wall and hoping a few of them stick.
On stage, the conventions of stand-up comedy change the stakes of Silverman's unique approach. She's crafty about meeting the joke-punch-line obligations to her audience, but she is always more compelling when she's found a way to subvert them.
In ''Jesus Is Magic," she pulls this off when she discusses sex and her body. Silverman can talk flippantly about a subject as a grave as rape without removing the horror of the transgression. The joke is not just in the act itself but in her devastated sense of irony. On those occasions, the clever blunt-instrument aspect of her comedy works. You can see the daring in her dare.
Wesley Morris can be reached at email@example.com.