n the Chinese zodiac, rats are considered witty, imaginative and curious. Now scientists have discovered another attribute.

A new study in the journal Science has found that rats can be helpful — the first instance that such behavior has been documented in rodents.

The researchers placed a free-roaming rat in an arena with a caged rat. Over the course of several days, the free rats realized they could nudge open a door and release the caged rat.

After figuring this out, they did so repeatedly, day after day.

“They then did what we refer to as a celebration,” said an author of the study, Peggy Mason, a neuroscientist at the University of Chicago. “The trapped rat runs around the arena, and the free rat appears excited and runs after the trapped rat.”

That behavior alone is not enough to show that rats are empathetic, she said. The rats could be releasing their caged cohorts simply for companionship.