The Kentucky Derby is this weekend. And fancy hats, desperate bets and eccentric horse names have everyone off to the races. But if you’ve had to relieve yourself recently, you may have wondered where the phrase I’ve got to pee like a racehorse came from.

Euphemisms for urination are sometimes bizarre and incomprehensible: See a man about a dog. A one o’clock appointment. Powder your nose. Answer the call of nature. Use the facilities. But pee like a racehorse may be more obvious to anyone who has ever actually seen a horse pee. If you haven’t, you’ll find that it’s quite the spectacle. Large mammals like horses produce quite a lot of fluid. The matter of racehorses in particular is still contended, though.

Racehorses and Furosemide

Some trace the logic back to an equine diuretic given to racing horses called furosemide (or by the brand name, Lasix). It has been used for many dubious reasons. But one side effect is a ‘flushing of the system’ which would impress anyone . Horses already have superhuman urinary abilities. But get a little furosemide in them, and they’ll flow like a fire hose that had one too many large ice coffees from Dunkin.

While this particular case might make the urinary behaviors of racehorses a feat to behold, others insist that it has nothing to do with racehorses specifically. They contend that the addition of race was just a “rhetorical flourish” used to emphasize the urgency of the matter .

It should be noted that in some circles, additional qualifiers are included like pee like a Russian racehorse. Or pee like a Chinese racehorse. These don’t seem to have any significance other than including a classic touch of racial insensitivity. During the Cold War, Russia took the brunt of western ire. And in present times China has fulfilled that role.