CBS's The Big Bang Theory panel at San Diego's Comic-Con wasn't full of too many surprises except for a prank that went horribly wrong. The cast wasn't able to talk about specifics pertaining to the upcoming 11th Season of the beloved show. But the panel started to liven up a lot more when the audience got its chance to ask the cast some questions. It wouldn't be Comic-Con without somebody asking Kaley Cuoco about her character Penny's last name to which she said "I have it in my head what I think it is, but now I'm Penny Hofstadter, so it doesn't matter what it is."

The panel also included stars Johnny Galecki, Kunal Nayyar, and Kevin Sussman and they shared some funny and tender stories, but the best story of the night came when Cuoco told a story about an on-set prank that went horribly wrong. The story comes to us from Entertainment Weekly who recounted Cuoco's story. It turns out that Galecki and Cuoco had decided to play a prank on the cast and crew while filming the Valentine's Day episode in Season 6 in which Penny and Leonard are fighting.

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Johnny Galecki and Kaley Cuoco decided ahead of time that they were going to take the fight a step forward and have Galecki punch Cuoco in the face. The two actors thought it would shock the cast and crew and make a good scene for the blooper reel, but that's not exactly how it went down. Galecki jokingly punched Cuoco in the face for authenticity, but her head accidentally hit the chair on her way to the ground. Galecki jumped on top of her and the two began to pretend fight not knowing that Cuoco had split her head open and was bleeding all over. Galecki even got some hair extensions from the hair and makeup team to make it look like he was ripping out Cuoco's hair.

Cuoco says, "So we did it and I fell over, and the chair, and no one knew this and I didn't either, clocked me in the head," Cuoco explained. "I just thought 'Oh, it's a little bruise,' but I'm still acting. I'm under (the table), and he's still punching me and throwing the hair, and I come back up and I'm like 'How did it look?' And all I see is Simon's face, and my blood is just gushing." The Big Bang Theory prodcuers brought along the actual video of the pretend beating going down and it looked pretty convincing. Cuoco is slightly out of the frame, so no blood is actually shown.

The gag did end in Cuoco having to go to the hospital to get stitches and the scene resumed filming on The Big Bang Theory the next day. Only one side of Cuoco's head can be seen in the subsequent episode because of her fresh stitches, which is completely evident when you go back and watch the episode. Cuoco finished by saying "We're not allowed to do those jokes anymore."