Perhaps it's because the comedian's face is still "numb" from the last time Momoa swung by the late-night show.
The "Aquaman" star made the "Tonight Show" host visibly uncomfortable on Thursday night before they had a little trident-throwing competition. While Fallon was announcing the premise of the game to his audience, Momoa paced around the comedian and stared him down with one of the sharp spears in hand.
It sent shivers down Fallon's spine, and the comedian tried to keep his eyes on his guest the entire time.
"In the movie, of course, Aquaman is a master of the trident -- where is he? Okay, there you are. Oh my gosh," Fallon nervously said while his body involuntarily braced for some kind of impact. "Dude. Oh my gosh. I'm telling you, I swear to God, every second I feel like you just might snap one of these days, and that's how it ends for me -- a trident."
Fallon pushed his nerves aside and got to the point: He and Momoa were going to throw tridents at targets for points.
You can take a wild guess as to who landed the most before watching the video below, but we will say it was a surprisingly close competition.
Perhaps Fallon's fear of Momoa stems from the last time the six-foot-four-inch action star stopped by the NBC late-night show. During the interview portion of the actor's appearance, Fallon reminisced about how painful their last game, Water War, was.
"I gotta say, I had no idea how strong you are," Fallon said to tee up clips from the game, in which the pair played the card game War with glasses of water in hand to douse the loser of each round.
Momoa, however, didn't just splash Fallon with water -- he whipped it at the comedian's face, and you can hear the impact.
"Dude, it sounded like somebody slapped a ham. It sounded like you smacked me with water," Fallon said after watching himself get whipped with water in slow motion. "I almost drowned. That's my drowning face."
"I have so many people come up to me and they're just like, 'That is the greatest thing ever," Momoa said.
"Dude it's the funniest thing ever," Fallon agreed. "I haven't played since, because my face is numb."
"Aquaman" hits theaters on Dec. 21. Watch the final trailer for the DC superhero movie below.