The 39-year-old actor's impressive strength once sent Game of Thrones showrunner David Benioff to the hospital, Benioff and D.B. Weiss revealed on Thursday's episode of HBO's web series, Backstories.
It all happened while the cast and crew were filming season two of GoT in Belfast. Momoa, whose Khal Drogo died in season one, returned to the series to film a dream sequence with Emilia Clarke. Afterward, he, Clarke, Alfie Allen, Benioff and Weiss headed out for some drinks.
"Jason was one of our favorite people ever on the show, and very strong. And that's not TV makeup -- in real life, he’s just a big, strong dude," Benioff began.
"So, I'm looking at Momoa and Momoa's talking about beating someone at the slap game," he recalled. "I was like, 'I'll take you at the slap game.' I was like, 'I'm going to challenge the Khal, because if I beat the Khal, I am the Khal.'"
A couple of beers in, Momoa and Benioff started playing the game, which consists of one player slapping the other's hands until they miss. Benioff quickly discovered he was no match for Momoa.
"I looked over and his hands were bright red," Weiss shared. "He was still going, and that was when all of us decided to put our conversation on hold to watch this contest."
"I looked in Momoa's eyes, I saw no mercy there," Benioff joked. "But I wouldn't quit, because, you know, I had my pride. I had my dumb pride."
Benioff's hands swelled up, and by the next morning, they had "doubled in size," he remembered. He headed back home to Los Angeles, hoping they'd go back to normal with time, but by the time he reached home, his wife, Amanda Peet, sent him straight to the hospital to get checked out.
"Her diagnosis was that Jason Momoa had squished my hands," Benioff shared, adding that he underwent a few X-rays. "So, it just goes to show, don't challenge the Khal."