All Hallow's Eve first originated as a Celtic Festival. The Celts believed that on Halloween night, the boundaries between the world of the living and the world of the dead converged. Their celebrations involved dancing around bonfires while wearing costumes comprised of animal heads and skins. Now, 2000 years later, the ritual of dressing up Halloween night remains and some of us even push this tradition onto our dogs. According to the National Retail Federation, Americans spent $350 million on Halloween costumes for their pets in 2016.