updated 08/03/2010 AT 9:00 AM ET
•originally published 08/03/2010 AT 5:00 PM ET
Eva Mendes and Will Ferrell play an unlikely married couple in their upcoming comedy, The Other Guys. But shooting an improvised argument scene together proved to be no joke.
“Once we got the scene down, we were told to improv,” Mendes, 36, told PEOPLE at the movie’s Manhattan premiere Monday. “We got into a little tug of war, and I picked up what was supposed to be a prop knife.”
Unbeknownst to the actress, “it was actually a carving knife from our meal. I lunged at him, and I was really proud of myself.”
Then she realized her mistake.