It turns out that hysterical fight scene when Lucy was stomping the grapes was not called for in the script. Lucille Ball and the actress playing her rival, Teresa Tirelli D'Amico, decided on their own to add it in when it came time to film (via Ranker). The year was 1956 and Ball remembered it 18 years later when she appeared on "The Dick Cavett Show" and explained what happened (via Cheat Sheet).

The producers had gone out of their way to hire Italian women who knew how to stomp grapes, but they only spoke Italian and didn't understand all the directions. Tirelli knew that she was supposed to have a fight with Ball, but that was it. When Ball accidentally struck her for real during filming, her on-screen rival took offense off-screen.

"So she hauled off and let me have it," Ball told Dick Cavett. "This was supposed to happen. That, she got right. But when she hit me, oh my God. She only came to about here [Ball's chest]. She hit me right [in the stomach] and took all the wind out of me."