MANKATO — The hardest part for the Bethany Lutheran College performers and directors isn’t:

Making a full house laugh three dozen times simply by having three student actors sit at a table on stage, wordlessly stacking a dozen cups for two or three minutes.

Coming up with the idea of doing Act 2, Scene 2 of Macbeth with Macbeth on Rollerblades and Lady Macbeth on a unicycle.

Testing the audience at a private religious school by recreating the famous Marilyn-Monroe-over-an-exhaust-grate pose — in this case replacing Monroe with Martin Luther, his frock billowing up to his waist just after putting his 95 Theses on the Castle Church door.

No, the hard part for the performers and directors at Bethany is explaining what the deal is with Theatre Physics — which is evident in the way the performance is officially entitled as “?Theatre Physics!”.

“It’s kind of ...,” actor Paul Blaschko says. “Not sketch comedy. It’s more physical comedy, vaudeville-style. ... It’s really an experiment in physical comedy and the physical aspects of acting in general.”

Blaschko goes to examples, running through the eclectic bits of the 13th version of the always-popular hour-long show, to try to define it.

Director Peter Bloedel, who kicked off the experiment 13 years ago and has been involved ever since, still can’t wrap his hands around Theatre Physics in a very concise way.

“It’s kind of theater in the raw,” Bloedel said. “... It’s kind of half-baked sometimes. It’s like theater in the microwave.”

Whatever Theater Physics is, the actors were cooking Sunday afternoon for the fifth straight sold-out show of the weekend. They wrapped up the hour with an extended skit on the proper care and feeding of zombies. Gross-out humor — involving a pair of zombies eating unpeeled oranges and limes without using their hands, a hand inexplicably stuck straight through a zombie’s abdomen, two women flossing a zombie’s esophagus — had the audience alternately groaning, gagging and laughing.

The performance’s reputation after more than a decade not only brings large audiences, it brings the most age-diverse group of spectators anywhere.

“You have the parents bringing toddlers in the first row, and college students in the back and my grandpa and grandma in the middle,” said Blaschko, a second-year student who ultimately wants to get a doctorate in play-writing.

Blaschko and the 10 other cast members stood in the lobby after ending the performance with a take-off on Riverdance, smiling as the still-laughing, still-energized audience exited. A cast party was on slate for the evening to celebrate what they’d pulled off in a little over two weeks of auditioning, writing, costuming, rehearsing and performing.

For Bloedel, his creation — transformed each year by the creativity of a new set of students — has come a long way from the opening performance 13 years ago when the theater was half empty. The word-of-mouth promotion of the show began that first night.

“A lot of them thought it was a science lecture,” he said of the initial audience. “The next night was a packed house. And it’s been full pretty much ever since.”