Chicago’s Rat Hole? Science concludes it’s likely not from a rat

For years, people in one Chicago neighborhood walked past an unusual sight: a hole in the sidewalk that looked as if a rat had belly-flopped into wet concrete. Dubbed “Splatatouille” — a riff on the name of the Disney movie Ratatouille — the Chicago Rat Hole went viral in 2024. Now research suggests that imprint is likely a squirrel squish.

The decades-old imprint became a sensation when artist Winslow Dumaine posted about the site.

After that, visitors left coins, flowers and other items beside the beloved landmark. They also shared plenty of pictures on social media. Those were key to a study published October 15 in Biology Letters.

In it, researchers borrowed methods from paleontology. They used fossil-investigating techniques to figure out which modern mammal made its mark in the city.

“It seemed like a fun project,” says Michael Granatosky. They got “to apply the scientific method to something that’s lighthearted.” Granatosky studies how evolution shapes the way animals move at the University of Tennessee in Knoxville. He was also part of a team who cracked the case.

A small mammal mystery

His group collected dozens of images of the rat hole shared on social media. From these, they measured features such as its nose-to-tail length and head width. Those data would help determine what actually made the critter crater.

Next, the team used the app iNaturalist. It identified eight small mammal species in Chicago. The researchers looked at measurements of museum specimens of those same eight species. Then they compared their sizes to those of the “rat hole.”

Splatatouille’s measurements most closely match those of a squirrel. What type? Most likely it was an eastern gray (Sciurus carolinensis) or fox squirrel (S. niger).

There don’t appear to be footprints leading to the imprint. So Granatosky suggests the animal likely fell into the wet concrete from above. Perhaps a bird of prey in flight — such as a hawk or owl — dropped the rodent. Or it may have fallen from a tree that residents say once stood by the mystery mammal mark.

Rat purists note that there’s no squirrel-like bushy tail in the impression. But Granatosky says it’s not likely that concrete would capture such fine furry detail.

The museum specimens and photos from social media gave the team a lot of data to work with. Yet the researchers still can’t be 100 percent sure what species made the beloved landmark. This shows just how hard it can be to analyze ancient specimens such as fossils. Granatosky hopes this case study will spark public curiosity.

“It’s so rare to get such a fun story,” he says. “It really speaks to what we do in my lab — which is take data and package it in a way that is accessible.”

As for the Rat Hole? It gained so much attention that some neighbors began to complain about the crowds on their quiet street. A few months after its initial fame, the city carefully removed that slab of sidewalk. But it’s not gone. Today, it sits protected in a display case at Chicago’s City Hall.