Want to trick a dog? It's all in the body language, a new study finds.


When given a choice between a big serving of food and a small one, dogs almost always go for the bigger option. But when a person makes a fuss over the small amount, particularly by handling it, dogs can be tricked into picking the less-hearty portion.


The study, published Wednesday (April 25) in the journal PLoS ONE, highlights dogs' ability to follow human social cues, a tendency which has likely served them well over thousands of years of domestication.


Researchers recruited 149 dog owners to bring their ordinary household pets into the psychology laboratory at the University of Milan, Italy. There, study leader Sarah Marshall-Pescini and her colleagues set up a series of experiments in which dogs had a choice between two plates, one with a single piece of food on it and one with six pieces. Other experiments had dogs choosing between equal-size portions.


In some cases, the dogs were allowed to pick a dish freely. In others, a person came in before the dog was allowed to make a choice, interacting with the food in some way. Sometimes the person would approach and stare at one of the plates; sometimes he or she would hold the piece of food near their mouth; and sometimes he or she would talk to the dog during the interaction.


The researchers mixed and matched these various conditions. For example, in some conditions the person merely looked at the dog and then at one of the plates. In others, the person might walk up to the food, pick up a piece and say, "Oh wow, this is good, this is so good!" while looking at the dog.


When left to their own devices, 73 percent of the dogs made a beeline for the bigger portion of food in the majority of trials. But when people started to get involved, the dogs were more often swayed to make the worse choice, going for the smaller food portion. The most powerful gesture for tricking dogs into making this choice turned out to be a hand-to-mouth action by the person. [What Your Dog's Breed Says About You]


Dogs in two experimental conditions were significantly more likely to make a dash for the small plate, the researchers reported. In one, the person approached the food, picked up a piece and held it to her mouth for five seconds before putting it down and retreating. In the second, the researcher did the same thing, except she also talked to the dog and looked at it as she held the food. When food was lifted and dropped with utensils from behind a curtain — so dogs couldn't see that a person was involved — the dogs were no more likely to pick that plate, suggesting that the animals are cueing in to human actions.


Dogs may see the handling of food as an explicit invitation to come chow down, the researchers wrote. Or it may be that seeing a person grasp a piece of food makes dogs want to do the same, much in the same way that babies imitate their parents' expressions and gestures. Earlier research has suggested that dogs are at least as receptive to human communication as are pre-verbal babies.


The study also highlights that imitation is not always the best strategy for learning, the researchers reported.


"The current study adds to a small but growing literature showing that social learning is not necessarily always the best strategy and provides an experimental paradigm which may potentially be used to explore when an animal will rely on private vs. social information," they wrote.


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