The researcher's experiment was well thought-out.

27 dogs were trained to recognize the difference between a kind woman who would give them their favorite kind of treat, and a mean one who would not. The women were labelled "cooperative" and "competitive" respectively.

The dogs were also presented with three containers. The first was filled each dog's favorite treat - sausage! The second had regular dog biscuits, and the third was empty. On the command "show me the food," the dogs would lead a woman to one of the containers. The cooperative woman would always give the dog a treat from whichever container they chose, while the competitive woman would not.

The dogs behavior was notably different towards the two women.

The dogs were far less likely to take the competitive woman to their favorite treat, since they knew she would keep it for herself. Two very smart dogs took the cooperative woman to the sausage every time, while never taking the competitive woman there.

The study, published in "Animal Cognition" states:

On both test days, the dogs were more likely to lead the cooperative partner than the competitive one to the box containing the preferred food, and this effect was stronger on the second than on the first test day.

After leading the competitive partner to one of the boxes, dogs were given an opportunity to lead the cooperative partner once again, thus giving the dogs an incentive to lead the competitive partner to one of the boxes even if they knew she wouldn't give them anything.

Researchers believe this shows dogs can display deceptive-like behavior.

The study's abstract concludes:

These results show that dogs distinguished between the cooperative and the competitive partner, and indicate the flexibility of dogs to adjust their behaviour and that they are able to use tactical deception.

However, the experiment isn't without its holes.

Skeptical minds point out that deception entails the dogs being aware of exactly what their partners want and "misleading" them. However, while humans will understand the words "show me the food" for its actual meaning, dogs may only hear it as a series of sounds that, to them, means "it's time to pick a container." In that case, they pooches will simply pick whatever they've learned will get them food, regardless of what the human "wants." The dogs may not even be aware they're part of a "deception."

Whether or not they're liars, one thing is certain: dogs are definitely a few notches smarter than we previously believed.

H/T - Indy 100, Animal Cognition