Canis coprophagicus

I understand that when you're a dog, the poorly-digested excrement of other animals can be the tastiest, most mind-alteringly delicious snack you've ever encountered in your whole entire life. What I cannot understand, Ripley, is why you must express your post-consumptive glee by licking as much of the exposed skin on my arms and hands as you can reach. Why, dog, why?