Ask them to do a trick, and they'll give it a try. For a reward, they'll happily keep at it.
But if one dog gets no reward, and then sees another get a sausage treat for doing the same trick, just try to get the first one to do it again. Indeed, he may even turn away and refuse to look at you.
Dogs, like people and monkeys, seem to have a sense of fairness.
"Animals react to inequity," said Friederike Range of the University of Vienna, who led a team of researchers testing animals at the school's Clever Dog Lab. "To avoid stress, we should try to avoid treating them differently."
Similar responses have been seen in monkeys.
Range said she wasn't surprised at the dogs' reaction, since wolves - the ancestors of modern dogs - are known to cooperate with one another and appear to be sensitive to each other.
In the reward experiments reported in today's edition of Proceedings of the National Academy of Sciences, Range and colleagues experimented with dogs that understood the command "paw," to place their paw in the hand of a researcher. It's the same game as teaching a dog to "shake hands."
Those that refused at the start were removed. That left 29 dogs to be tested in varying pairs.
The dogs sat side by side with an experimenter in front of them. In front of the experimenter was a divided food bowl with pieces of sausage on one side and brown bread on the other. The dogs were asked to shake hands, and each could see what reward the other received.
When one dog got a reward and the other didn't, the unrewarded animal stopped playing. When both got a reward, all was well.
One thing that did surprise the researchers was that - unlike primates - the dogs didn't seem to care whether the reward was sausage or bread.
