A new interview with Billy Crystal, who voices Mike in Monsters, Inc. and the upcoming prequel Monsters University, reveals that he and John Goodman (Sulley) have to record together – a rare technique in animation – to get the chemistry right.

Voice actors do not usually record together, and Crystal has a problem with that. “If one person [records their lines] before the other, you’re laying down the rules for the scene,” Crystal says in an interview with USA Today. “It’s not spontaneous, particularly when you improvise as much as we do.”

Once Crystal and Goodman recorded together for the first time on Monsters, Inc., there was no going back. “His voice is just too big, too good to go off a recording,” Crystal said. “You need to be in a room with the guy to get the chemistry.”

Added Goodman, “We really like to get physical and play off each other. It helps you connect with the character you’re playing. After two hours of recording, I’m wiped out. It’s like we played a rugby match.”

Elsewhere in the interview, Crystal noted that there’s a lot of pressure on him and the studio to pull off another win because Pixar has had 14 number one films in a row. He also said that he’d be open to the idea of a third Monsters film, but if they do it, he doesn’t want to wait twelve years like he did in between Inc. and University.

In addition to these new comments, we were treated to three news photos. They may be scenes from the new Monsters University trailer premiering tomorrow, April 25th.

Monsters University opens June 21.