LOS ANGELES — Jack Black discovered the painful part of acting through his role in the action movie spoof "Tropic Thunder."

The work that left him bruised now can be seen on DVD.

In the film within the film, Black plays one of a group of actors filming a big-budget war movie. An attempt by the director to give the production more of a real feel puts the actors in a real battle for their lives.

One scene called for Black to work with a not-so-accommodating female water buffalo. Black debated being in the movie because he had concerns about how his character was to be draped across the beast's back. But director Ben Stiller persuaded him to do the scene.

Black's first instincts were right. "We would do the scenes, but I could tell she was agitated. At one point she flipped my (expletive) off of her," Black says during an interview for the theatrical release of the comedy. "Miraculously it was a safe landing between some boulders."

It wasn't Black's fault. No one knew until later the water buffalo was pregnant. The calf was given the name Little Jack.

"I also bruised a rib in another scene," Black says. "I was running with my big gun, and I dove into a foxhole.

"I landed funny on the gun, and it bruised my rib. That bruise lasted six weeks. You cannot breathe all the way without it hurting."

But through it all, Black says, filming the 2005 "King Kong" was far more demanding physically on him because of the long shooting schedule, location filming and special effects.

But he felt less acting pressure because of the large ensemble cast that included Ben Stiller, Robert Downey Jr. and Tom Cruise.