At Custer State Park, they have a Wildlife Loop Road that is fun to drive. It is slow-going, but nice scenery. There is a particular spot where the wild burros hang out, and children love it. Great for photos.
I was cutting through the park on one of the back roads to get to a prospecting area that I wanted to check, and encountered a traffic jam. A single-lane road with about twenty cars all stopped. Coming at us, the Park Rangers were on horseback, driving a huge herd of bison of a couple hundred head. Bison don't leave "road apples" like horses; they leave "cow pies". What a mess on that road.
Bison also have no fear. They are huge and will fight a mountain lion if provoked. The only warning you get if they are annoyed with you, or if you are between them and their baby, is that they will raise their tail like a flag. If you don't leave immediately, they will charge you. Many people have died at Yellowstone Park trying to pet the "fluffy cows".
Anyway, as this herd was meandering by all the vehicles, one of them decided they didn't like the front of my truck and tried to head-butt it. He was unsuccessful in moving my truck, so he went around me. I blew a raspberry at him as he went by.