What does a dog waggling its tail signalize? Well, most of us have the experience that a strong tail waggle means a happy dog. But according to a study done by an Italian team of psychologists lead by Vallortigara, there is more information present in the waggle and its dependent on the direction of the movement, not only the force.
For the experiment, the scientists, confronted thirty dogs of various breeds to four sets of stimuli: their owner, an unknown person, a large Belgian Shepherd Malinois and a cat.
Then they measured the strength and direction of the tail waggling. It turned out that as expected, the strongest response was elicited when the dog was presented their owner or the dominant dog. Interestingly, the predominant direction of the waggling in the two instances was opposite: right when seeing their owner, left when seeing the dominant dog.
The way the direction and amplitude of the tail waggling were measured.
These results provide an example for behavioral asymmetry in animals and contribute to the theory that left and right parts of the brain are specialized respectively for approach and withdrawal processes.