Dogs don't relieve themselves facing just any direction - they align themselves along the magnetic north-south axis when urinating and defecating.

This is according to a study published in the journal Frontiers in Zoology. In it, the researchers analyzed the body orientation of 70 dogs of different breeds during more than 7,000 observations, including just under 2,000 instances of defecation and nearly 5,600 instances of urination, during a two-year period.

Vlastimil Hart, from the Czech University of Life Sciences, and Hynek Burda, from the University of Duisburg-Essen, sifted through the results in hopes of identifying some kind of pattern. At first, there appeared to be none. Unlike cows, foxes and deer, all of which align themselves on a north-south axis, the canines seemed to relieve themselves in whatever direction they pleased, with no thought as to where they were facing.

This changed as the scientists began to sort through data on slight variations in the geomagnetic field that took place during the study period. As they did so, a picture began to emerge. Dogs, they found, align their bodies along the magnetic north-south axis only when the geomagnetic field is calm. This was true even when taking into account other factors, such as the dogs' familiarity with an area, the time of day or weather.

That the results were so surprising only adds credence to the study's integrity, the researchers argue.

"The study was truly blind," they wrote in the study. "Although the observers were acquainted with our previous studies on magnetic alignment in animals and could have consciously or unconsciously biased the results, no one, not even the coordinators of the study, hypothesized that expression of alignment could have been affected by the geomagnetic situation, and particularly by such subtle changes of the magnetic declination." Magnetic declination refers to the difference between true north, or the axis around which the Earth rotates, and magnetic north.

What remains unclear, however, is whether the decision to align is done consciously or not. It's possible, the authors write, that the dogs perceive the magnetic field sensorially, and that after sensing it, they are able to respond to it. Another option they propose is that the animals are unconsciously responding to a sense that one direction simply feels better than the other.