In September 2021, Oscar Isaac and Jessica Chastain were the stars of a viral video from their appearance at the Venice International Film Festival in 2021 to promote their show "Scenes From a Marriage," where the pair seemed maybe a little too comfortable with each other. 

In the viral video, the two were posing with their arms around each other for photos. Nothing seemed out of the ordinary until Isaac appeared to kiss and sniff Chastain's underarm area. Isaac recently spoke on SiriusXM's "The Jess Cagle Show" where he offered an explanation for the odd sniffing by comparing himself and Chastain to flatworms. 

"You know, you can cut them into like a hundred pieces and they will grow a whole new worm out of the little piece. So they're basically kind of immortal and they've been doing work at the cellular level where they're seeing that the cells kind of talk to each other through electricity and kind of decide, ‘Okay you're going to make the head.' ‘All right, I’m going to make the tail'…they're communicating through some sort of electro kind of magnetic situation," Isaac explained. 

Oscar Isaac kissing Jessica Chastain upper arm

While at the Venice International Film Festival, it seemed as though Oscar Isaac was kissing Jessica Chastain's upper arm.  (Elisabetta A. Villa/Getty Images)

JESSICA CHASTAIN HAD ONE CONDITION WHILE FILMING FULL-FRONTAL NUDITY: ‘I WANTED IT TO BE BALANCED’ 

Now, how does all of that related to the interesting behavior between the two actors? The ‘Moon Knight" actor said it’s because that whole process is similar to how he and Chastain communicate with one another. 

"Maybe we should use more actual human language to talk instead of sniffing an armpit and doing things like that," Isaac said. "That's kind of what starts to happen and no matter how much we annoy each other, no matter what happens, it's like, when you get us together, it's like, it's just other stuff that's going on that is making us grow two heads." 

Chastain talked about this moment last September on the "Today" show, but had a much simpler explanation for the strange situation. 

Jessica Chastain and Oscar Isaac

Jessica Chastain and Oscar Isaac starred in the HBO television drama "Scenes From a Marriage." (Elisabetta A. Villa/Getty Images)

"We have all been locked in our houses for so long. When this video went viral, I was like, ‘people just need to see people touch and hold each other," "The 355" actress explained. She also talked about how the two went to college together and have been friends for a large portion of their lives and do know each other extremely well. She touched upon they know each other so well that they can "almost read each other's minds."