Parsons says Sheldon’s union suit, while completely out of the ordinary, have only one affect on him. “In a weird way, it didn’t affect anything except, ‘I need a bigger shirt,’ ” he says, noting that the long johns made for a long day on the set. “Two weeks ago I was in a French maid costume and that I talked themdown from. They wanted to put me in the Princess Leia slave uniform in a bikini and I said, ‘No, I’d need six months’ warning and a personal trainer and it’s not happening.’ They were very sweet to me and said, ‘OK, we didn’t know what your boundaries were.’ (Laughing.) Maybe Season 7 if we’re around and I can prep for it.”

Jim Parsons prepares for a scene in which Sheldon sports a pair of long johns — aka a union suit — to prevent the spread of the germs that (naturally!) lurk in rental tuxedos as the guys are fitted for Howard’s wedding to Bernadette. “As an actor, I’ve always had a very distinctive relationship with costumes,” Parsons says. “One of my favorite things in the world is costumes because they speak things that you don’tneed to speak. They change a character just by putting something on but what’s great about them is they can have their own life.”

During a scene where the guys are being fitted for tuxedos, the writers added in a line of dialogue to reference Sheldon’s favorite comic book character, The Flash, taking advantage of his red long johns. “The Flash rewrite was a really good example of when the writers come in with changes in a scene,” Parsons explains. “It’s an inspired choice. There is a certain level of inspiration that only strikes when the gun is to your head in a weird way. You feel that was an example from the writers, that wasn’t a difficult joke to make but it couldn’t be made until it was in the moment because it was a reflection of the costume which they hadn’t seen fully until then,” Parsons says of the new line. “Just looking on camera, it’s ‘This would work perfectly here.’

Parsons says the addition of Bialik’s Amy stands out as his “favorite thing that’s happened in the past year and a half of the show.” “The introduction of Amy as a character has brought many possibilities for Sheldon. I enjoy working with Mayim and it would be my personal preference that she never be allowed to work with anybody else,” he says with a laugh. “She should do all her scenes with me! That said, it wouldn’t be good for her or the show and in the end it wouldn’t be good for me but that’s how much I enjoy playing those scenes with her in all their different and strange forms.”

Photos from behind scenes: