Dogs would rather defecate along the Earth's north-south axis line instead of the east-west axis, according to someone who had the time to study dog butt preferences.
The research—which was carried out by a team of Czech and German scientists over the course of two years and 1,893 piles of poop—found that dogs are sensitive to small variations in the Earth's magnetic field. During times of "calm electromagnetic weather," they consistently choose to crap while facing north or south. Not only that, but they actively avoid east/west crapping.
But for as much as they've studied how dogs poop, scientists still don't know why they do it that way.
It is still enigmatic why the dogs do align at all, whether they do it 'consciously' (i.e., whether the magnetic field is sensorial perceived (the dogs 'see,' 'hear' or 'smell' the compass direction or perceive it as a haptic stimulus) or whether its reception is controlled on the vegetative level (they 'feel better/more comfortable or worse/less comfortable' in a certain direction).
However, this study only applies to dogs pooping freestyle, without being on a leash. So it's all just a bunch of shit.