A mule deer "poggos" when it runs although they also trot too. A mule deer’s under belly, especially near the chest is black and with whitetails with me anyways, the first thing I see is bits of white from their lower stomach and their tail (which they often flick and wag when they're walking like a dog) moving.A mulies tail is narrow with a black tip and the top of a whites tail is brown and bushy.