Dogs use the Earth's magnetic field when they're relieving themselves. Not only that, but canines choose to do so in a north-south axis, a new study published in the journal Frontiers in Zoology says. The study suggests that dogs are sensitive to small variations in Earth's magnetic field. After examining 70 dogs -- made up of 37 breeds -- over two years, 1,893 defecations and 5,582 urinations, researchers found that under "calm magnetic field conditions,"