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Tom Cruise can't keep a straight face during Mad Lib Theater with Jimmy Fallon

Tom Cruise visited The Tonight Show Starring Jimmy Fallon where he played a little "Mad Lib Theater." And after coming up with some great words, the two tried to perform a spy thriller scene. But from the very start, Cruise found that keeping a straight face was nearly an impossible mission.

Fallon spent about 5 minutes mining random words from Cruise, some of which were intrinsically funny, like "doodie head."

Cruise is either a great sport or has had little exposure to Mad Libs because he could not stop laughing during the sketch. It took him several seconds to gather his composure just to get his first line out.

Fortunately, by the time he got to his last line the 3-time Oscar nominated actor was able to reign in the laughter and explain how his character became such a good spy. He said, "By waking up every morning, going up on the roof, and kissing, and by repeating my own personal mantra -- poopity-scoop, poopity-scoop."

If you'd like to see Cruise perform some real acting in real spy film, Mission: Impossible - Fallout opens July 27th.

The Tonight Show Starring Jimmy Fallon  airs weeknights at 11:35 on NBC. Watch clips and full episodes of The Tonight Show for free on Yahoo View.