They may look pretty outside your window, but icicles shouldn't be messed with. In addition to killing at least 15 people in the U.S. each year, the ice formations contain nasty bacteria. So unless you're interested in ingesting bird poop, it's best not to treat them like a popsicle.

In a TikTok video reported by BuzzFeed, meteorologist Katie Nikolaou explains why icicles aren't as crystal clean as they may appear. The ice that freezes on the outside of your home comes from water trickling off your roof. Birds like to hang out on top of houses, and where there are birds, there's bird poop.

@weather_katieDon’t eat icicles! Please respect the fact that I edited out the original woman in the video (I have her permission) #IciclePoop

♬ original sound - nickolaou.weather

Even if it doesn't contain fecal matter, water may come into contact with twigs, bugs, and dead leaves before freezing. Imagine licking your roof: If that thought grosses you out, you shouldn't be putting an icicle anywhere near your mouth.

A much healthier way to channel your enthusiasm for the weather this winter is to learn more about it. Here are some cool facts about snow you should know.

[h/t BuzzFeed]