"Camp X-Ray, very serious, very dark," Fallon said of the Twilight star's latest work. The late-night host wanted to "lighten the mood a little," so he brought out a wacky diversion for the two: plastic elephant masks and a pile of rings.
"Every time you come on, we like to play a game!" Fallon continued. "[This is] called 'Ring Around the Nosey.' It's the most fun game ever… You're just gonna love it, Kristen, I swear. You just get so happy."
Stewart, 24, put a mask over her face and started smiling. She sarcastically joked, "It's so much better than looking sad!" The premise of the game was then explained by Fallon, who told his guest: "First person to get one ring on their nosey, winsies the gamesies."
Also during her appearance, Stewart old the late-night host that she adopted a puppy while filming. "I was at work and a buddy of mine I usually work with was playing frisbee golf, and he found these guys. He told his brother who was driving me at the time that he had to have a really serious conversation with us."
The actress found it strange. "I hate when people are like, 'Hey, dude, I need to talk to you,'" Stewart revealed. "All of a sudden he erupted into a euphoric smile, like just looked so happy. I was like, 'What is the deal?' And he opened the door and there were these two little babies, and I was just like, 'Oooooo!'"
The proud star added of her puppy Young Cole: "She's the best dog in the world. LIterally, she's the coolest dog."
Watch the video of Stewart above!