During the audience Q&A session, one fan asked, "Are there pranks on set? Or surprises you plan for each other?"
Kaley then recounted the prank that she and Johnny Galecki attempted to pull but went terribly wrong.
She began, "Our gag reels are very funny, the Valentines Day Episode for Season 6 and the scene was us fighting (Johnny) and so we thought it would be funny if we took it way too far and Johny would punch me for the gag reel. And set it all up and called makeup to get extensions so that it would freak everyone out... and so we did it, but I fell over and the chair flipped over and hit me in the head, but we didn't know it did anything, and so Johnny kept going with fake punching me."
Continuing, she recalled, "And then when we came up from it my head was busted open and my real blood was everywhere and everyone was panicked. So then I had to go get stitches and we had to reblock the shot. So if you watch the show, I am faced in another direction because I had stitches."
The Big Bang Theory panel was hosted by Riki Linghome (who plays Ramona Nowitzki on the show) and John Ross Bowie (who played Barry Kripke on the show), and featured Kaley Cuoco, Johnny Galecki, Kunal Nayyar, Kevin Sussman, plus a trio of writers and trio of producers.