The problem is, anticipating the appearance of wild animals, and also what they are going to do. Deer can rush out across the road, and if startled by a vehicle, can turn to rush back - this is exactly what happened to my daughter when I was with her a year ago - about 500yds from Tesco, on the bypass, not traveling too fast in my opinion.
I've had muntjac running in front of me through our village when I've cycled home from the pub!
Deer seem relatively robust - you ronly occasionally see dead ones on the road - we couldn't find the one my daughter hit. Maybe they are the type of animal that makes for cover no matter how badly injured they are.