To size up what might make chickens happy in their brief lives, researchers at the University of Guelph in Ontario, Canada, are putting 16 breeds through physical fitness and behavioral tests. They’re watching how well birds scramble over a barrier for food, how skittish they seem and whether they play with a fake worm.

Chickens can’t say how they feel, but playing with a fake worm may be a sign of happiness.

“We have to infer when an animal is happy or content or experiencing pleasure based on their behavior,” said Stephanie Torrey, one of the researchers.