A few years ago, two Michigan urologists noticed a curious pattern among their patients: Upon returning from a Disney World vacation, patients would report they had passed a kidney stone after riding Big Thunder Mountain Railroad. (Yes, seriously.) Now the doctors are actually studying the phenomenon — complete with their own, um, interesting trip to Disney World — and they've turned up some surprising results, The Atlantic reports Approximately 10% of people will get kidney stones (small mineral deposits in the kidneys) at some point. Although most people pass them through the urinary tract without any noticeable issues, some stones become large enough to cause a ton of pain when they exit. (The pain of passing stones is often compared to that of childbirth.) That, plus the unpleasantness of bloody urine and also nausea, often sends people with kidney stones to the ER. So, being able to prevent these stones (usually by drinking enough water every day) — or at least getting them through your system before they get that big — could save you pain as well as money spent on healthcare. It could even preserve your sanity.For the study , forthcoming in the October issue of the Journal of the American Osteopathic Association, the researchers managed to take a model of a kidney (tucked safely into a backpack) that was full of real, diluted pee on Walt Disney World's Big Thunder Mountain in Orlando, FL. The researchers decided that if the fake kidney's fake kidney stone was dislodged and made it to the fake ureter (where urine normally passes from the kidney to the bladder), that would count as "passing" the stone.