Matt Damon revealed why kissing Scarlett Johansson was “hell” one time while they were filming their 2011 family comedy “We Bought A Zoo.”

The 52-year-old actor and his “Opppenheimer” co-star Emily Blunt were discussing proper etiquette for shooting kissing scenes with co-stars in a recent video for LADBible. The two strongly agreed that tooth-brushing, using mouthwash and chewing gum was mandatory though Damon noted that he could “forgive some halitosis.”

During their conversation, the “Good Will Hunting” star recalled a less than pleasant onscreen smooch that he once shared Johansson, 38.

“I had to kiss Scarlett Johansson — can you imagine how horrible that was for me?” Damon joked.

Matt Damon recalled kissing Scarlett Johansson on the set of their movie “We Bought a Zoo” after she ate an onion sandwich. (Jim Spellman/WireImage)

“Can you imagine how awful that was?” Blunt quipped. “It’s such a shame she has such terrible lips and everything. It must have been so awful.”

“It was hell!” the “Saving Private Ryan” actor said with a laugh.

He continued, “What happened was, we did a sH๏τ before lunch, and it was this nice little two-sH๏τ that ended in the kiss. And it was really good.”

“We went to lunch, and she and I both thought it was over, and she ate like an onion sandwich for lunch,” Damon remembered.

“She came in, and [director] Cameron Crowe had set the camera up, and it was like a тιԍнт sH๏τ of the kiss,” the Mᴀssachusetts native recalled. “And she goes ‘Aw s—!  She goes, ’I literally just had, I had like an onion sandwich. I thought we did this.””

“The Devil Wears Prada” star jokingly asked Damon if he was “still sort of slightly aroused” by kissing Johansson despite her bad breath.

“No, I was making fun of her that entire time about her onion breath, which I didn’t even smell,” Damon said.

“Her breath smells like roses,” Damon insisted as the pair burst into laughter.