Jack Black discovered the painful part of acting in the action movie spoof "Tropic Thunder," now out on DVD.

In the film within the film, Black plays one of a group of actors filming a big-budget war movie. 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.

"We would do the scenes, but I could tell she was agitated. At one point she flipped [me] off of her," Black tells the Fresno Bee. "Miraculously, it was a safe landing between some boulders."

No one knew until later that 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 Black says that filming 2005's "King Kong" was more demanding in many ways because of the long shooting schedule, location filming and special effects. Although there was pain in "Tropic," it put less acting pressure on Black because of the large ensemble cast that included Stiller, Robert Downey Jr., Matthew McConaughey and Tom Cruise.

"I had a great time just watching the other guys do their thing and then stepping up to take my crack at bat once in a while."