Going back through my catalog, I find that this is one of my favorite photos taken during my drive up to Alaska. Let me set the scene for you:
I started the day just outside of the Grand Tetons National Park and I had finished spending the better part of 6 hours in Yellowstone. By that point it had begun to snow heavily and I realized that I needed to get a move on or else risk getting stuck in the park when I needed to end the day a few hundred miles to the north. Up to that point, I hadn't seen a single large mammal in the park and I was basically resigned to the fact that I wouldn't see any in Yellowstone. Suddenly, within the last 10 miles of road before leaving the park, a herd of bison appeared, grazing on the side of the road. Disregarding the rules of the park, I stopped right in the road (luckily it was November and very few other cars were around), did a super fast lens swap and snapped this photo from my driver's seat. I was probably about 15-20 feet away from the bison.
330mm 1/125sec F5.6 ISO 1600