Matt Damon is opening up about kissing Scarlett Johansson onscreen — and it didn’t quite go the way one might expect!

In an interview for LADbible TV with his Oppenheimer costar Emily Blunt, the 52-year-old actor recalled sharing a smooch with Johansson, 38, for their 2011 dramedy film We Bought a Zoo, during which the actress wasn’t quite prepared breath-wise.

“We went to lunch and she and I both thought [filming the kissing scene] was over and she ate, like, an onion sandwich,” Damon told Blunt, 40. “And she came in and [director] Cameron Crowe had set the camera up and it was, like, a tight shot of the kiss.”

“And she goes ‘Aw s—! I literally just had – I had, like, an onion sandwich,’ ” he said, laughing.

The conversation, which was about whether you should tell someone they have bad breath or keep mum, began when Damon said he “had to kiss Scarlett Johansson” for the movie.

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“Can you imagine how horrible that was for me?” he joked.

“It’s such a shame — she has such terrible lips,” Blunt quipped. “Must’ve been so awful.”

“It was hell,” he joked in addition.

After Damon shared the story about the onion sandwich, Blunt playfully pressed him, “But were you still sort of slightly aroused getting to [kiss her]?”

In the end, “I was making fun of her the entire time about her onion breath, which I didn’t even smell,” Damon replied, adding with another laugh, ” ‘Cause her breath smells like roses.”

Damon’s onion-laden kiss with Johansson was just one anecdote from the set of We Bought a Zoo, in which the actors played a pair who connect after Damon’s widower character acquires a new home with his children that also includes a zoo on the property. (Johansson plays a zookeeper whom Damon’s character develops a relationship with.)

As the Black Widow actress told PEOPLE at the movie’s New York City premiere in December 2011, the scariest moment on the film was watching a “terrified” Damon “cry like a baby and rock back and forth when the snakes were spread all over the set.”

“He was definitely sweating a bit, and maybe the sweat formed in the corner of his eye,” she added. “I said, ‘Matt, these kids are practically juggling the snakes. Hold it together.’ ”

“I’m afraid of snakes,” Damon admitted to PEOPLE. “And I got bullied into interacting with them by Scarlett and the kids.”

Oppenheimer is in theaters now.