Chicago’s viral ‘Rat Hole’ is less rat splat, more squirrel squish.

Researchers determined it was probably a squirrel that left a rodent-shaped impression in the concrete of the Windy City. Their new study, published October 15 in Biology Letters, borrowed paleontological tools to analyze the bizarre and beloved local landmark.

Michael Granatosky, an evolutionary biomechanics researcher at the University of Tennessee in Knoxville, was motivated to study the decades-old imprint shortly after artist Winslow Dumaine posted about the site in 2024. Dubbed Splatatouille, the Chicago Rat Hole quickly became a viral sensation, with visitors to the city’s Roscoe Village neighborhood leaving coins, flowers and other paraphernalia before the slab was moved to City Hall. Despite Chicago’s status as the “rattiest city in America,” the culprit has long been questioned.