A calm chat between Conan O'Brien and Jack Black turned into epic guitar showdown when the actor and Tenacious D  frontman stopped by "Conan" on Wednesday (Dec. 22).
After talking about XBox and Black's new movie, "Gulliver's Travels," things got heated at the clip's 6:30 mark, when the actor sounded surprised to hear O'Brien refer to his musical riffing as a "band." "I think of your band as more of a hobby, and less like a passion," Black told the talk show host, adding, "I rock way, way, way harder than you."
Eventually, the two funnymen strapped on their guitars (Conan goes electric while Jack stays acoustic) and started noodling around. The competition was a dead heat -- until Black pulled back the curtain behind them and reveaied that Slash  had been playing O'Brien's part for him backstage.
O'Brien isn't the only late night host Black has been challenging musically this week: the comedian stopped by "Late Night with Jimmy Fallon" to perform "Little Drummer Boy" with the help of some multi-colored paint. Watch:
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