April 26, 2013 at 12:35 PM ET
Does anyone have more fun on set than "The Big Bang Theory" cast and crew? Last fall, the gang delighted a live audience and its writing staff with an impromptu "Call Me Maybe" flash mob that went viral, and other behind-the-scenes stunts always make for a wildly entertaining gag reel each season.
But sometimes, as star Kaley Cuoco said Wednesday on "Jimmy Kimmel Live," their pranks can go terribly awry.
After finishing a scene for this season's Valentine's Day episode, in which Leonard and Penny get in a fight, the actress explained that she and her mischievous partner, Johnny Galecki, decided to provide some extra footage for the gag reel.
"We decided to do a (surprise) prank where Johnny punches me," the blond beauty revealed. At first, everything seemed to go "perfectly": "I go flying off the chair, the chair comes after me…the writers are laughing, Chuck Lorre's laughing, everyone's cracking up."
But under the table, Cuoco wondered whether she took a genuine hit.
"I kinda feel like something's throbbing," she said, but was most concerned about whether Galecki's roundhouse "looked real." She got her answer when she stood up and was covered in blood.
"Everyone thought I was under the table painting blood on my face, (but) I had cracked my head open," Cuoco shared. "I had blood squirting down my face. I didn't even know!"
She took it in stride; her "sensitive" castmates not so much. "We don't have a very macho group of people … Johnny's in tears, Simon's vomiting in the corner, the blood is gushing down my face. I was amazed at how much was on my face … I thought it was the most awesome thing in the world."
Not so awesome? The six stitches and black eye on her face, which coincided with the SAG awards. "So I decided to have the brilliant idea to wear (fake) bangs … because it covered my black eye and I was really insecure."
She felt even worse when critics slammed her "helmet-style hair." "It was honestly the worst-reviewed hair in history," she said, quoting some of the reviews. "These bangs … almost ruined my entire career!"
But with Kimmel's help, Cuoco was finally able to "say goodbye forever" to the hairpiece: They attached the fake fringe to a bunch of helium balloons and sent it skyward from the studio.
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