A young woman is found lying on the dusty floor of an abandoned barn, her once-beautiful face now horribly disfigured. Where her nose and teeth used to be is a grisly mess of bone and flesh with a single imprint of a horseshoe being the only recognizable aspect of her hideous features.

With nowhere else to turn, Dr. Examine, the plastic surgeon-come-criminologist, is called in to investigate. He concludes that the woman has been the victim of an international horse conspiracy in which ponies are given to people as gifts, then are trained to attack them when they look into the mouth of the animal.

The moral of the story? Never look a gift horse in the mouth.

Perhaps it's not quite the caliber of Agatha Christie or Stephen King, but it's the best that Spontaneous Combustion, Penn State's improvisational theater group, could come up with in its frantic spur-of-the-moment rehersal last Sunday as they prepared for tonight's performance.

"This last rehersal shows us what's working and what isn't," said Jill Bamford (junior-theatre arts), the group's assistant director, referring to the selection of scenes to appear in the final product.

The group's style of improvisation and audience participation makes for an exciting and unique theater experience.

"You can never tell what's gonna happen," said Zack Buchanan (sophomore-theatre arts), a group member. "It really depends what the audience gives you and how quickly you can work with it."

There is no basic outline for the show, explained Rebecca Dreyfuss, Spontaneous Combustion director. All of the skits are created on the spot by suggestions from the audience, then developed ad-lib by the players. The rehearsals are basically geared at honing these skills and organizing the line up and order of the show, she added.

But the real organization lies in choosing which actors to put in which skits, said Dreyfuss (junior-theatre arts). In certain skits, the combination of actors is crucial to the flow and appeal of the scene, she added.

"Every one of (the actors has) specific abilities, and each 'game' uses different skills -- that's why the last rehearsal is always so hectic; last minute changes need to be done," Dreyfuss said.

Nervous as they may be, however, the actors are quietly confident about the upcoming performance.

"Its gonna be a good show, definitely," Buchanan said. "We usually get a few laughs."

Buchanan's improv skills will be put to the test in two of the five skits that make up the one-hour show. And if Sunday's rehearsal is anything to go on, the group should receive a lot more than just a few laughs.

Compared to traditional theater, improv is a true rarity. There are no costumes or elaborate sets to hide behind if the actor cannot come through -- not even a script to fall back on. The performance is theater at its purest; a stage and a voice, nothing else.

The group -- which usually performs late at night -- has been forced to schedule an earlier performance this evening because new University Resident Theatre Company policy now restricts the use of the Arts Building late at night.

Although the policy may change the type of audience they will get, Dreyfuss said the group members are still confident of a great performance.

Spontaneous Combustion will perform a free show at 5:45 p.m. today in 118 Arts.