Early morning commuters got a surprise when faced with a random, secret door in the middle of Chicago Union Station.
A sign asked passerbys to take a peek at what was behind “Door number one,” and it shocked just about everyone that jiggled the doorknob. Hundreds of mini brightly colored balls tumbled out and onto the floor, causing laughter, smiles and gasps of surprise.
It’s all park of a larger ball pit door prank that is catching on across the nation. In January 2015, a college student imported 13,000 mini balls from China and stacked them in his bedroom.
Watch the behind-the-scenes video of this prank to find out how organizers managed to pull this off.