A comedy of terrors on Ben Stiller's set

The best comedy is based on reality, says John Hamburg, director of the latest Ben Stiller vehicle, "Along Came Polly." "But we just take it a bit further than what happens to most people in normal everyday life," he adds.

As if to underline the point, his star and co-writer, Stiller, points out that one of the cast members bit him on the lip during filming. And, no, the incident didn't occur during an on-screen smooch with costar Jennifer Aniston, who plays the role of Polly. The nibbler in question was Polly's pet, a frisky ferret.

"It was really weird," says Stiller, who plays an upright risk analyst who falls for the free-spirited Polly. "It did this crazy turn thing and literally attached itself to my chin - and then it didn't let go," he says, grabbing his mouth to illustrate the point. "It was this surreal thing, where like, OK, the ferret's on my chin."

At a press event for any other film, the conversation no doubt would've moved on to other things. But this being a Hamburg/Stiller reunion (previously, they wrote two of Stiller's biggest hits, "Meet the Parents" and "Zoolander"), the ferret routine rolls along into a whole new realm of comic potential. Stiller makes the observation that "they are rat-like creatures."

"It's just a big rat at the end of the day," agrees Aniston. At that moment, a woman in the press corps with neon-tinted hair stands up to reveal a T-shirt illustrated with ferrets. She objects to the way the stars are characterizing what are clearly her favorite pets.

"You're wearing a bunch of ferrets on your T-shirt," says Aniston, looking at the woman. "I'm so sorry, I should have looked closer." To which the woman replies, "Jennifer, I don't know if you are aware of this, but you are in Ferrets magazine this month." Aniston, looking more like a deer caught in headlights, says "I didn't even know there was a Ferrets magazine. That is very exciting."

Not even a three-way chat among Vanilla Ice, Tammy Faye Bakker, and Erik Estrada on TV's "Surreal Life" gets quite this weird. The entire exchange has an air of the sort of frantic, off-keel surprises that real life can deliver at a moment's notice - and that Hamburg and Stiller specialize in exploiting.

In "Along Came Polly," for instance, a man with a delicate stomach eats far too much spicy food and ends up in a bathroom with no toilet paper ... in his new girlfriend's house ... where the only available resource is a delicately embroidered lace handkerchief, which immediately backs up the toilet.

"We don't deliberately set up absurd situations," says Mr. Hamburg. "We try to remain true to the characters and see where that takes us."

In "Polly" this sensibility follows Stiller's character, Reuben Feffer, as he loses his bride on his honeymoon, to a naked scuba instructor; plays racketball against a risk-taking CEO who specializes in extreme sports; and faces off (literally) against a large, sweaty, and very hairy opponent in a pickup basketball game on a particularly hot, Manhattan day.

"What I look for are the normal situations that anyone might be in," says Hamburg, "and I take them to the comic extreme, making them worse and worse."

The director says he allows his actors to improvise. Often, the invented moments remain in the film. But equally, he says there are times when what he calls "the music of his comedy" prevails and the scene is filmed as written.

"I trust my director," says Stiller, who admits he is frequently embarrassed by his screen antics but says there isn't anything he wouldn't at least try. "It's all on a case-by-case basis," he says. "If it doesn't work, it won't be in the movie."