The Umbilical Brothers perform smart slapstick with the hyperactive glee of oversized kids. At the family-friendly New Victory Theater, where the duo’s latest show “Speedmouse” opened on Friday night, their slaphappy energy spread through the young crowd like a sugar high.

But if the Umbilical Brothers have terrific showmanship, they’ve also got great technique. While the expert physical clown David Collins is ducking and dodging his way through a breakneck sequence of jokes, his partner Shane Dundas is matching Mr. Collins’s every move with an unbelievable array of sound effects. All that Dave (as he’s known in the show) has to do is press down his index finger, and the unmistakable sound of an aerosol spray can instantly issues from Shane’s mouth. The technique is a fascinating riff on a vaudeville tradition: It’s the old ventriloquist act meets human beatboxing.

Indeed, the Umbilical Brothers work like an old-time traveling vaudeville troupe, keeping their best sketches and adding to them over time. Some of the bits here will be familiar to people who saw “Thwak,” the team’s 1999 off-Broadway show (which played the New Victory again in 2003.) But “Speedmouse” also includes some entirely new gags. One involves a remote control that can rewind, fast-forward, or pause the onstage antics — a device that pays off in an inspired freeze-frame of Shane flipping Dave the bird.

Shane and Dave, it should be noted, are a couple of Australian guys who are pretty relaxed about low-level naughtiness. Though they’ve “installed a censor” for their New Victory appearance (generating their own bleeps), there are a few times when, as Shane notes, the bleep comes a little too late. And there’s plenty of raucous humor in the show, like the laugh-till-you-cry puppet show in which a bunny clobbers a koala. A recurring subplot involves a surly “roadie” in a clown costume who brings out the childish worst in Dave.

A clown costume? Yes, and a lot of mime and slapstick and sound effects — and a lone piece of green posterboard, the show’s only real prop. If the Umbilical Brothers are a little rough around the edges, that roughness is ultimately inseparable from their charm. In a hightech age, what makes these two so exhilarating is their ability to make you howl with laughter merely by using their voices, their bodies, and their brains.

So when they (briefly) wander over into the arid territory of Yoda and Arnold Schwarzenegger impressions, you want to shake them by the shoulders. Heaven forbid the Umbilical Brothers should leave the road less traveled. Their wondrously inventive, deliciously silly physical comedy is a rare species in a world dominated by the easy, bland joke.

***

Groovelily is a solid three-piece New York studio band that tours a lot. Brendan Milburn handles the keyboards, the redhead Valerie Vigoda plays the electric violin, Gene Lewin is on drums, and all three of them sing pretty well. And that’s probably the way things should have stayed. But one day, while on tour, they decided to do “something that would be a cross between a rock concert and a holiday show for people who don’t really like holiday shows.” This fateful decision produced “Striking 12,” a new musical at the Daryl Roth in which the three musicians simultaneously sing, play, and act their way through a derivative, flyweight holiday show.

It is hard to imagine what motivated Mr. Milburn and Ms. Vigoda to team with the writer Rachel Sheinkin on the story of an unnamed, mildly depressive guy who doesn’t want to leave his apartment on New Year’s Eve. (In a weirdly honest intro, Mr. Milburn admits they wanted to do a show that would let them stay in one place for a while.)

Suffice it to say that 15 songs later, the antisocial guy does go out into the street, where the “snowflakes fall like velvet/from iron colored skies” and he “feels his spirits rise” on “the first day of the new year.” But not before he’s had a chance to read Hans Christian Andersen’s “The Little Match Girl” out loud, and complain about the kind of co-worker party where people’s idea of small talk is,”Did you mean to CC me on that e-mail?”

It may be true that a lot of people can relate to the experiences so generically (and leadenly) described by “Striking 12”: the bad parties, the bad “Law & Order” episode, the bad Dilbert job. But even if one grants “Striking 12” a kind of holiday special-waiver to deal in trite commodities, its Scrooge is a pretty poor specimen. With his trendy hipster shirt and his indoor stocking cap, Mr. Milburn’s character is supposed to be some sort of hard-core thirtysomething cynic, but surely there are much darker specimens of downtown nihilism in any car of the L train.

Nor does “Striking 12” somehow redeem its mundane setting by some stunning reversal. In the end, Mr. Milburn breaks through his malaise by buying light bulbs from a door-to-door salesgirl (Ms. Vigoda) who distributes brochures on seasonal affective disorder. And the band rocks out on a chorus of “The Little Drummer Boy,” backed by a tableau of Christmas bulbs artistically suspended on strings.

The performers bravely throw themselves into the cabaret-style acting, and they deliver the songs with skill and verve. But the songs themselves are as anemic as the show — musically, they’re in the zone of Michael McDonald, with lyrics that make a beeline for the obvious. In the end, you just end up feeling sorry for these likable performers. There’s nothing more disheartening than a feel-good show that makes you feel bad for it.

“Speedmouse” until November 26 (209 W. 42nd St., between Seventh and Eighth avenues, 212-239-6200); “Striking 12” until Dec.31 (101 E.15th St. at Union Square East, 212-239-6200).