If they lingered too long over the pictures of the men, and did not move on swiftly enough to the pictures of the women, they received an electric shock.

After scientists showed the four crows a series of colour photographs of humans with their hair concealed, one pair was trained to pick men's faces and the other pair women's faces.

Holding their partner’s hand or viewing his photo decreased the women’s painsignificantly more than touching or viewing a stranger—and the photo was justas effective as the physical contact.