It's not just dog feces they will roll in or eat. Many dogs do this and it is actually common. Many times you may not notice if they are only eating it, rolling in it is usually is noticeable on their coat. My dog once rolled on a dead skunk. Why? The smell. Along with smell sometimes it is the undigested protein that triggers food when they smell it. But no one seems to have a clear cut answer to why dogs do this. That seems to be the answer that has become popular when this topic is brought up.