This photo was tweeted by user lyxopk on Wednesday night and it's been retweeted over 14,000 times since.
Lyxopk — who asked to keep her real name private — lives in Brooklyn and told BuzzFeed News the photo was taken by her friend in the boys' bathroom of her high school.
"There isn't really a story," she said. "The boys in my school always do pranks like this. Last year, it was goldfish in the toilet."
The photo, though, has started a giant argument about whether it's a toilet full of onions or a toilet full of red cabbage.
"It looks like onions to me and friends, but a lot of people are saying it's cabbage," she said.
Lyxopk said her school has tried closing the bathrooms on one floor for a few weeks, but it hasn't stopped kids from pulling pranks. "At the end of the day, it's just extra work for janitors," she said.
So if you're thinking about filling toilets with onions at your own school, just please, think of the janitors.
Teenagers are weird.
Ryan Broderick is a reporter for BuzzFeed News and is based in London.