The improv strengths of the current Second City comedy troupe inspired a new format. Clockwise, from left: Martin Garcia, Bridget Kloss, Craig Uhlir, Amanda Blake Davis and Seamus McCarthy.

Veterinary proctologists. Mexican softcore porn. Bacchus and Dionysius. Space Dolphin. Abe Lincoln. The Steve Miller Band.

All these things have something in common. They all surfaced within a single performance of The Second City's new all-improvised comedy format. And all of them were funnier in the moment than any attempt to explain them after the fact could be.

The improv show is 70 minutes of "You had to be there." The laughs are as absurdist and transitory as a dream. Memories of the material vanish almost as quickly as the audience can file out of the small Flamingo showroom.

The comic ensemble is trying something new here as it closes in on five years in Las Vegas, blending two forms of improvisation. The first is the "game" format that's been part of previous Second City editions. The slapstick, quick-hit charades and guessing games hit prime-time in "Whose Line Is It Anyway?" and live on in Las Vegas visits by the TV show's cast, including Colin Mochrie and Brad Sherwood next weekend at the Las Vegas Hilton.

The second is so-called "longform" improv that hasn't had much stage time on the Strip. It's usually saved for the aspiring actors of Los Angeles or for "second stages" of bigger cities with established improv troupes. It minimizes the game structure and lets the spontaneous scenes play out more theatrically.

This local move is a bit puzzling, to have in essence a second stage but no first one. Sketch comedy has been Second City's claim to fame since 1959 -- "Saturday Night Live" and "SCTV" both sprang from the Chicago-based institution -- so it seems a shame not to see any here.

(Well, for one day you can. The new show takes today and Saturday off so The Comedy Festival can use the room. But the same troupe does a special show at 5 p.m. Saturday to perform classic Second City sketches for the festival.)

On the other hand, the audience seemed tuned in to the new format, offering some of the complicated suggestions listed above along with simple ones, such as airports ("a place people gather"). Most of all they responded to the winning teamwork of the five players, whose improv strengths motivated the change.

Nothing can throw this bunch. Playing a sexually transmitted disease? No problem for Martin Garcia. "Yeah, I got two kids. One's called Strepto. The other is called Coccus. My wife's name is Chlamydia."

Given the chance to venture into bad-taste territory with the suggestion "Special Olympics referee," Bridget Kloss instead shrugs to Amanda Blake Davis and says, "What are we doing here? Everyone's a winner." Fade to black.

The airport suggestion lined up all five cast members to step out one at a time and create characters. Davis was an immigrant who lives in the terminal after seeing the Tom Hanks movie "The Terminal." Craig Uhlir was a baggage handler: "One day, when we were bored, one of my friends bet me I couldn't put on everything that was in the suitcase."

Even more impressively, the characters come back later, along with characters from other bits. The players conspire backstage, jotting their ideas for tie-backs on a chalkboard.

Experienced improv director Liz Allen also keeps the show under control with structuring that's not immediately obvious.

The show may be different each night, but it will always parody a daytime talk show, with Kloss pulling two audience members onstage. (On this evening, the crowd members were either aspiring improv actors themselves, or thought they really were in a daytime shoutfest.) There is always a moment where a washed-up rock singer (Garcia) will make up a song with a title supplied by the audience. This time it was "I Love My Bald Head."

The format puts the audience at the risk of a lesser chemistry on nights when one of these top-notch players -- including Seamus McCarthy, the only member of every Las Vegas edition -- has a day off.

Beyond that, the only real sacrifice is the careful pacing of previous outings, replaced by a rapid-fire barrage that yields a lot of singles and doubles, but not as many home runs as the written stuff.

That's OK. It's the effort of the players that you will remember.