“The Big Bang Theory” was all about comedy and jokes, both on and off-screen. Unfortunately, practical jokes of any kind came with a real-life hazard warning thanks to the actions of co-stars Johnny Galecki and Kaley Cuoco in Season 6. While speaking at San Diego Comic-Con (via the Toronto Sun), the on-screen love interests and real-life exes admitted they were the reason pranks had to be banned on the hit sitcom’s set.

While filming Season 6, Episode 16, titled “The Tangible Affection Proof,” the two planned to pull a prank that involved Galecki fake-punching Cuoco. “We thought it would be really funny for the gag reel to take it really far,” Cuoco said — but their plan went awry. While this could have easily been one of those bloopers that make us love Kaley Cuoco even more, the “Charmed” alum ended up getting injured for real, making the prank far less funny than planned.

After Galecki pulled his fake punch, Cuoco fake fell off her chair. At this point, she hit her head for real, though she didn’t realize at first. She explained that when she got up, she was excited to celebrate how brilliantly they’d pulled off the prank. “We did it. (When I got up) all I see is blood gushing out of my head… it was all over me!” The day ended with a trip to the hospital for Cuoco, and it had consequences for the entire set. “I had to get stitches that day and come shoot the next day. I got back and there were signs that said, ‘No fun allowed on the Big Bang set.'” This ended up being one of many rules the cast of “The Big Bang Theory” had to follow, whether they were working or just hanging out on set.

It seems that Kaley Cuoco and the cast of “The Big Bang Theory” observed the no practical jokes — or “no fun” — on set edict after the unfortunate chair incident, but that didn’t stop Cuoco from pulling pranks while working on other projects. While filming the thriller “The Flight Attendant,” which ran for two seasons on HBO, Cuoco took to Instagram to share some of the hijinks going on behind closed doors. In fact, she detailed one of the most heinous tricks ever played on her, which came courtesy of her make-up artist, Jayde Moon.

Moon took it upon herself to decorate Cuoco’s bathroom with fake cockroaches, though they clearly looked enough like the real thing to completely freak Cuoco out. The star turned around and started screaming the minute she saw the fake critters, as her assistant caught the hilarious reaction on camera. “It never ends. I live in constant fear around here lol,” she wrote alongside the video, which she posted on her Instagram Story (via Nicki Swift).

Unfortunately for the TV star, that was far from the end of the on-set pranks. The entire cast and crew repeatedly teamed up to get one over on her. “This is literally every day. The cast and crew has plotted against me and now scares me at every turn. I am not safe,” she explained. The final straw came when someone replaced her initials on her personalized set chair with the word “stupid.” “Large reward for whoever tells me who did this.” Cuoco wrote when she shared details of the prank, though she never revealed if she found the culprit.