So Wartinger compiled people’s stories, and he realized that the common factor was having ridden Big Thunder Mountain Railroad. He found anecdotal reports of people passing stones after bungee jumping, but no research on this bodily-movement approach. So he decided to take things into his own hands and do a proper study.

First, Wartinger used a 3-D printer to create a clear silicone model of that three-time-stone patient’s kidney. He then filled the kidney with stones and urine. (Not real urine, I assumed, as I know the park already has plenty.) Then he and colleague Marc Mitchell bought two tickets and flew to Orlando.

Of course, the researchers had to get permission from Disney World before bringing the model kidney onto the rides. “It was a little bit of luck,” Wartinger recalls. “We went to guest services, and we didn't want them to wonder what was going on—two adult men riding the same ride again and again, carrying a backpack. We told them what our intent was, and it turned out that the manager that day was a guy who recently had a kidney stone. He called the ride manager and said, do whatever you can to help these guys, they're trying to help people with kidney stones.”

Other parks, Wartinger says, “have reacted anywhere from lukewarm to really not sure what to do with us.”

The two held the backpack between them “at kidney height” to try to subject the model to the same forces that a person would experience. A stone was counted as “passed” if it moved from a starting location lodged in a calyx and fell down into a trap at the point where the kidney meets the ureters. None of the stones or fluid actually spilled out during the roller coaster ride. (The research protocol notes: “Care was taken to protect and preserve the enjoyment of the other guests at the park.”)

“What was amazing was within just a few rides it became obvious that there was a huge difference in passage rates whether you sat in the front or the rear of the coaster,” Wartinger tells me. “There was a lot more whipping around in that rear car.”

The stones passed 63.89 percent of the time while the kidneys were in the back of the car. When they were in the front, the passage rate was only 16.67 percent. That’s based on only 60 rides on a single coaster, and Wartinger guards his excitement in the journal article: “Preliminary study findings support the anecdotal evidence that a ride on a moderate-intensity roller coaster could benefit some patients with small kidney stones.”

Now, though, he has done more than 200 total stone rides on Big Thunder Mountain Railroad. But that doesn’t mean it’s the only coaster that could be therapeutic: “Some rides are going to be more advantageous for some patients than other rides. So I wouldn't say that the only ride that helps you pass stones is Big Thunder Mountain. That's grossly inaccurate.”