Mount Poo-suvius: Watch What Happens When You Flush a Toilet Without a Lid

While indoor plumbing remains one of the great innovations of modern civilization, it can still come with some caveats. Things can get clogged, hot water heaters can burst, and toilets can spray bacteria-ridden poop plumes upon flushing.

That latter asterisk is one reason people are urged to close the lid of the toilet before flushing. Now, researchers at the University of Colorado Boulder have managed to demonstrate just what kind of aerosolized feces we’re dealing with.

According to Smithsonian, the team struck upon the idea of aiming green lasers at a toilet, dimming the lights, and letting cameras capture the now-illuminated particles ejected during flushing when they scattered the laser light. Their work, published in the journal Scientific Reports, is titled “Commercial toilets emit energetic and rapidly spreading aerosol plumes,” which gives you a hint at what happened.

As you can see in the video above, it’s quite the show. Particles shot nearly 5 feet into the air and some were suspended for as long as a minute. Others settled on the wall surrounding the fixture.

“We had expected these aerosol particles would just sort of float up, but they came out like a rocket,” lead author and professor of civil, environmental, and architectural engineering John Crimaldi told CU Boulder Today.

As depositories of human waste, toilets harbor a variety of illness-causing bacteria and viruses, like E. coli. A lidless toilet expelling them into the air creates a theoretical opportunity for those germs to be inhaled—not only from the occupant’s drop-off, but from the countless others who have used the facilities.

Researchers didn’t use any actual feces in the experiment, only clean tap water, which could possibly affect the speed or trajectory of the particles. (“The presence of fecal matter and toilet paper could alter plume dynamics in unpredictable ways,” reads the paper, which sounds ominous.)

Nor did they examine how particles might travel on a closed-lid toilet with only a small seam around the edges. But the overall message seems clear: Public bathrooms are grosser than previously believed, and when you go at home, keep a lid on it.