The real stories behind the craziest (and grossest) medical cases on Grey's Anatomy

If there's ever been a hospital to encounter more hair-raising, gruesome, downright crazy medical cases than Grey Sloan Memorial (formerly known as Seattle Grace and Seattle Grace Mercy West), then we'll eat our ferry boat scrub cap.

The good doctors of Seattle have encountered everything from a man with tree hands (definitely don't eat snacks while viewing that episode) to a man with a fish trapped in his penis to a girl who could feel no pain (which she proved by having a classmate hit her in the stomach with a baseball bat).

If it's rare and even ridiculous, the staff at Grey Sloan have treated it. "We're the 1 percent hospital," jokes executive producer and emergency medicine resident Zoanne Clack. "Fitting rare medical cases into the characters' stories is a total puzzle."

Whether to further a storyline or reveal something new about a character, every bizarre medical condition that rolls into the hospital on the gurney is a metaphor for what's happening at that moment in season's arc. With daily briefing from medical researchers explaining the most recent goings-on in medicine (from journals, papers, and news stories around the world), the writers' room sets about fitting the case into the storyline, making sure it brings certain characters together to move the story forward.

"We have a file of strange, mysterious, fun, and interesting cases to draw from, and sometimes we'll have the episode going and someone will be like, 'I really love a certain story, now let's try to frame the personal stories around this medical thing,'" Clack explains. "Sometimes we have to scrap the case because we can't make it work for that particular character's story. Other times we think, 'What is the case that we could do that would put these two characters together because we need them in a room to discuss the problem of the week?' We then take something from our pool, or we have a lot of physicians here at the show who can draw from their own experiences. Or we'll make something up and then make sure that it works with experts."

"We really wanted something that would stand out on X-ray," Clack says of the writers' choice to have a man ingest doll heads. "We were just researching all different kinds of ingestions that people did and wanted it to be something that wouldn't kill them right away. A lot of people will swallow paperclips and knives — which we did later with a prisoner. So that's what we came up with because it would be such a funny-looking X-ray."

"We realized that there are certain hormones and things that are released when you watch porn," says Clack. "We also wanted to introduce the pain-management storyline, with Derek being the doctor who dealt with it. So we just pushed them together and had that happen. It also gave us that moment where Cristina realizes, 'This works scientifically, so now I'm going to try and work with it.'"

"That was absolutely fabricated," Clack says. "We usually have one big impalement a season, and this was obviously one of the first and the biggest. In the room, the conversation was about the Derek/Meredith relationship and tearing people apart and making a choice, so we came up with the two people impaled together. Then we had to figure out the trajectory of the pole, how they would still be talking, how we would move them, etc. We had two of our married writers be our models to make it less awkward. They sat together and I could see where the pole could go and what organs it would go through and how it could affect them but still have them talking. There was a lot of modeling that went along with that. It was fun to figure out."

"I was really excited about that one," says Clack. "One of the big learning curves I had to make on early seasons was trying to open up my mind and not say no to writers' suggestions all the time. This one was one of the ones where my initial thought was, 'Are you kidding me? We can't do this!' But then I realized that a teratoma puts out the hormones that you make during pregnancy. Then we thought to have him do a pregnancy test with his wife who is actually pregnant, and if it's positive he can truly believe that he's pregnant. That was a major coup, a major feather in my hat to figure out how to actually make it work medically."

"That was something we read," says Clack. "It's definitely from a journal article — this woman who needed to get this surgery because she was having spontaneous orgasms. We tried to get it in a couple of episodes before it actually landed. We kind of kept that one to the side because we wanted to put it where it belonged, where it would fit with the story."

"That was definitely from an article," Clack recalls. "We heard about the case and the writer immediately latched onto it, and we were just trying to figure out how far we could go with this girl, thinking of all the different possibilities of how she would get injured. Making her this fearless person definitely helped with what was going on in the episode, story-arc-wise."

"When this one was suggested, I was like, 'Are we able to do that, theoretically?'" remembers Clack. "I had to go away and figure out how that could be possible and just figure out if it was theoretically possible, even if it's never actually happened. It's always just thinking, 'How do we make this work for the story we want to tell?'"

"This one was very, very complex, and it was very much about having to do that big of a surgery for love," says Clack. "It was also all about us wanting to use a bunch of surgeons all at once. We wanted it to be complex and we wanted it to inform on the love triangle [Derek-Mark-Addison], and it just seemed to work — and, of course, we wanted it to be kind of funny."

"We couldn't make that up!" Clack says. "It happens; the fish will follow the stream of urine into the penis. This was a case we read about in season 1 or 2 and literally tried to put it in three or four episodes. It would always fall out because it wasn't grounded enough, or we had too many stories and we had to let go of one. We finally accomplished it! It was one of those Grey's Anatomy lore kind of cases that we kept on the board, kept in the room and we'd be like, 'What about penis fish for this story?!' It was in so many episodes before the one it ended up in, it was hilarious."

"That came from the mind of [series creator] Shonda Rhimes," shares Clack. "That was one that actually took a long time to research because it doesn't really happen. We were trying to figure out the effect of cement on the body from smaller cases, where it's happened on arms or legs or whatever. The main point of that was to get all of our characters together. We actually use it as a framework for cases that we do now when we need everyone together. We're also always looking for stuff that's visual when it comes to the hospital — like the guy whose hand was stuck in the meat grinder — because obviously they take care of a lot of stuff in the field and it's not as visually interesting when it gets to the doctors."

"We've had people who, from our episodes, have diagnosed themselves or their children or are very appreciative because they wouldn't have pushed as hard or asked their doctor about certain stuff," says Clack. "After the girl-with-the-hole-in-her-ear episode, we got a message from a mom who had a 6-year-old son experiencing symptoms like that, and they finally went to the ENT and asked for him to be tested for this. They tested him and he had it and [they] cured him, and he's great now!"

"Like penis fish, tree hands was in the ether for a long time, and [executive producer] Mark Wilding was the one that pulled it off," explains Clack. "It was based on a real case. A little boy actually had this disease and went to go and get it treated in India or somewhere, and then they grew back again. There was a lot of video and footage about this boy to use, and we talked to a bunch of experts about it. It was really interesting because I really didn't even understand how warts turn into that. We also had to figure out how this could happen in America, because the little boy that it had happened to was in this little remote village on some island [and] so didn't have access to care. So we had to base our premise on the character's reclusive backstory, and then we were able to pull it up and use it."