The star was there to promote his upcoming thriller, Nightcrawler, but Fallon had other plans for what he wanted to do with Gyllenhaal, a game of water war.
"I'm here with Jake Gyllenhaal," Fallon began, "and we're going to have a water war."
"We're playing the card game war, but if you lose the hand, you get a pint of water in the face," Fallon explained. "We each have five glasses of water; the first one to throw all five glasses on their opponent wins and then gets to water cannon the loser."
The pair took a seat opposite each other with a small table between them, and they then took turns to splash water on each other's faces based on the draw of a card (yes, we were secretly hoping Gyllenhaal would lose so we could see him in a wet shirt).
"Lots of ways to get wet and only one way to win," the funnyman added.
The host and the Prisoners actor were not the only ones fighting back giggles as they engaged in a full-on water war. And Gyllenhaal was a really good sport about everything, even if he did think the game was "totally fixed!"
The result? Both the funnyman and Gyllenhaal were left drenched!
BTW, Nightcrawler opens in theaters on Friday, Oct. 31.
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