Dogs have an intuitive understanding of fair play and become resentful if they feel that another dog is getting a better deal, a new study has found.

The study, in the Proceedings of the National Academy of Sciences, looked at how dogs react when a buddy is rewarded for the same trick in an unequal way.

Friederike Range, a researcher at the University of Vienna in Austria, and her colleagues did a series of experiments with dogs who knew how to respond to the command “give the paw,” or shake. The dogs were normally happy to repeatedly give the paw, whether they got a reward or not.

But that changed if they saw that another dog was being rewarded with a piece of food, while they received nothing.

Who’s a good dog?  You’re a good dog!  Oh, what a lover gives me kisses.  Thump you like a melon!  Okay, no more kisses on my glasses!  Sit!  Want to go out?  You do?  Oh, let’s go out, you good dog!