07/03/2013 at 12:00 PM EDT
The Melissa McCarthy who showed up to the Boston set of The Heat
last summer with her two young daughters in tow could have passed for a friendly out-of-towner. Polite. Unassuming, even.
"A sweet midwestern mom," as costar Michael McDonald puts it. But then the cameras starting rolling – and McCarthy morphed into a "beast," says castmate Bill Burr.
The same woman who "doesn't even swear in real life," notes Heat
director Paul Feig, "gets into character and suddenly the F-words start pouring out."
Wildly uninhibited, profanely funny and unafraid to use "everything in her toolbox," as Feig puts it, to get a laugh, McCarthy now finds herself in that most exclusive of showbiz stratospheres: an Oscar-nominated, Emmy-winning superstar with a hit sitcom (CBS's Mike & Molly
) and a big-screen summer smash (The Heat
, costarring Sandra Bullock
, which raked in $40 million during its opening weekend).