Hemsworth was up first, and his supposed confession was, "My first job was cleaning out breast pumps."
After Fallon and Nanjiani grilled him for 45 seconds trying to poke holes in the story to figure out its validity, the handsome Australian superstar revealed that it was, in fact, the truth.
"I literally worked for a pharmacy, and they would rent them out and the machines would come back and I would have a toothbrush, a little spray-and-wipe," Hemsworth recalled, with a shrug.
The actor, who said he also had to repair the motors in the pumps, explained they'd need to be cleaned after they came back "covered in dry milk."
"Do the women who use these breast pumps now know that Chris Hemsworth once cleaned them?" Nanjiani asked. "And can you buy them on ebay?"
Hemsworth wasn't the only one with a surprising confession. When it came around to Nanjiani, his secret -- which he revealed was true -- was, "I once tried to murder someone in Singapore."
When asked how he tried to do it, Nanjiani shrugged, "Strangulation. Pretty standard."
Although, it turns out not to be quite as sinister (and potentially criminal) as it sounds. He was around 10 years old and he was sleepwalking.
"It was my aunt. And I had little 10-year-old hands, so I never had a shot," the comic recalled. "But I was never allowed to watch horror movies as a kid, and I was staying at her house, and she was like, 'It's fine, I'll show you one. What's the worst that could happen?' And then I tried to murder her, in my sleep."
"I don't remember any of it, but I remember that things were weird at breakfast," he added.
Hemsworth and Nanjiani's new film, Men In Black: International, also starring Tessa Thompson, Emma Thompson and Liam Neeson, hits theaters June 14.