Stars Scarlett Johansson and Chris Evans told "Nightline" that when they were filming "The Avengers" in Cleveland, Ohio, they went to a local bar to blow off some steam, and Johansson wound up on stage singing "Rocky Raccoon."
"It was a dive bar. It was in the middle of nowhere. There must have been no more than 20 people in the whole bar," Evans, who plays Captain America in "The Avengers," told ABC's Chris Connelly.
"On the stage was this band, this real broke-down band, and [Johansson] said, 'We should get up there and sing 'Rocky Raccoon.'"
"Always a good karaoke song," said Johansson, who plays Black Widow in the film. "The singer, I think she just had one too many and she was just, like, done…and I was like, 'This is somebody who's got to do something about this.'"
Evans said Johansson then asked one of the guitar players if he knew the song "Rocky Raccoon."
"She got up on stage and just started singing," he said. "Not only was she amazing, the whole bar got into it. I didn't even think they knew who it was…but that's Scarlett. She's got a wild streak in her. She's adventurous."
"I thought Evans was going to join in, you know, his love for musical theater and all," Johansson joked back. "That's a little-known fact about Chris Evans… he's a big singing-dancing enthusiast."
As much fun as the cast had off-set, they said working together on set was a blast.
"Then when you get Robert [Downey, Jr.] and Tom Hiddleston into the mix, it just plummets. It's a zoo," Johansson said.
"You get nothing done," said Jeremy Renner, who plays Hawkeye in the film.
And if "The Avengers" director Joss Whedon wanted to get their attention? "He would clap and scream and say, 'Children!'" Renner said.
"Yes, he'd be like, 'Kids, kids,'" Johansson said. "We were like an unruly classroom."
Whedon compared directing "The Avengers" cast to "herding adorable kittens."
"I had to use my teacher voice," Whedon said. "The only problem I ever had was that when they were having so much fun together and I was trying to roll and they were supposed to fight. You're supposed to be arguing, not loving each other."
"The Avengers," which is produced by ABC News' parent company, The Walt Disney Company, premieres in theaters nationwide on May 4.
Watch the full interview with "The Avengers" cast on " Nightline" TONIGHT at 11:35 p.m. ET