Dogs are quite possibly the most uncouth creatures ever to stalk the Earth. Their instinctive attraction to filth, decaying carrion, and biological waste of every sort is remarkable. This is one of the reasons that cats don't like dogs and usually regard them with mixed horror and contempt, but it's only one of many such reasons. It would take a thick book to list all of them.

My Dachshund has a Masters in vomit detection and a PHD in filth acquisition and carrion disposal, and he's proud of it.