'Avengers' Stars Scarlett Johansson and Mark Ruffalo on Laughing at Hulk's Leotard (Video)

Despite the number of distinctive or memorable characters that populate the world of The Avengers, much less the team, the Hulk is probably the scariest. A physical manifestation of Dr. Bruce Banner’s anger, he wreaks havoc among his fellow heroes as aggressively as he torments Banner’s psyche. But actor Mark Ruffalo said that the biggest challenge of playing the Hulk was not feeling silly while he wore the motion-capture costume that technicians later used to transform him into the massive green monster.

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“I’ll never forget the first day I walked on set in my little leotard,” Ruffalo told THR. “Immediately I saw half of the crew and cast start to giggle. But when I freaked out I was actually pretty scary.”

Despite the fact that Ruffalo struggled to intimidate his co-stars – not to mention that his performance in the film as Banner is downright adorable – Scarlett Johansson, who plays Black Widow, said that the filmmakers provided her with a more tangible adversary to square off against.

“What happened was that they had this guy for the height, because he had to be running,” she revealed. “So they had this guy that was like seven feet tall, and they painted him green – and he was absolutely terrifying.”

With such a large ensemble of characters, all of whom have complex mythologies that not only could but probably need their own individual films, it would be understandable for the actors to worry that they might not have much to do in The Avengers. But any worries that Ruffalo or Johansson had were soon assuaged by Whedon’s script, which divided screen time remarkably evenly.

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“I think Joss Whedon did such a great job of balancing the storylines,” Johansson said. Ruffalo agreed: “He really tried to give each person their due moment in the sun, and it’s pretty incredible that he was able to weave all of those stories together.”

Watch the video above for more detailed insights about Johansson and Ruffalo’s experiences making the superhero team-up film. The Avengers opens nationwide on May 4, 2012.