Babies learn lots of things about the world by copying adults but they learn surprisingly quickly which people to trust.

In tests with 60 babies aged 13 to 16 months, researchers found that a baby will stop copying an adult if it thinks it has been previously tricked by the grown-up.

Testers were split into two groups: ‘reliable’ and ‘unreliable’. In the first part of the study, the testers would look into a box and pretend to be excited, then let the babies copy them. In the reliable group, the box contained a toy, but the unreliable testers used an empty box.

For the second part, testers pushed a light on with their forehead. In the reliable group, 61% of the babies copied the movement, but only 34% of infants with an unreliable tester tried to turn the light on.

“This shows infants will imitate behaviour from a reliable adult,” says researcher Ivy Brooker. “In contrast, the same behaviour performed by an unreliable adult is interpreted as irrational or inefficient, and therefore not worth imitating.”