Melissa McCarthy Reveals the One Word that Always Made Rose Byrne Laugh

The Spy actress says she loves making her costar crack up on set

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One of the hardest parts of comedy is keeping a straight face – and Melissa McCarthy takes great pride in making her costars break character on set.

And her Bridesmaids and Spy costar Rose Byrne is one of her favorite – and easiest – targets.

“When we did Bridesmaids I kind of really, really always went after Rose because she’s a big laugher,” McCarthy tells PEOPLE and Entertainment Weekly editorial director Jess Cagle.

“She’s also a terrible laugher because she will just completely break down in a scene.”

And during filming, there was one simple word that had Byrne in stiches every time.

“For some reason, whenever I would say “Helen” in Bridesmaids she could not stop laughing,” McCarthy remembers. (If there’s anyone out there who still hasn t seen this movie, Helen is Byrne’s character’s name.)

Once the cast and crew caught on, they “were all rooting for it, so then I would start saying “Helen” at the front middle and end of every sentence,” McCarthy explains.

“She’s so sweet and she’s so beautiful, that’s it really fun to try to like, verbally destroy her,” she adds.

Related: Melissa McCarthy and Jess Cagle Chat about Wigs

McCarthy says another on-set laughing culprit is her Spy director Paul Feig, who she says is prone to chuckling “full volume” during takes.

At least with Feig, the actress jokes, cracking up is more acceptable, “because you know it’s going well.”

Spy opens in theaters June 5.