We hit a dog once by an acreage - good size Lab that just ran out of the tall ditch grass in front of me, never had a chance to stop.
The family was out in the yard, they saw it happen, I pulled over immediately hoping for the best, walked back to where the dog was and apologized profusely to the owners. They were very understanding and said this wasn't their first dog to get hit living on a highway. Don't get me wrong they were still upset, as was my family.
This happened probably 5 years ago and I still think about it every time I drive past that place.