Critters like deer and elk become accustomed to regular vehicle and pedestrian traffic on a trail or road. If something happens that deviates from that, like stopping, or getting out of a vehicle, they tend to respond by moving away. Back in the early 80's CPW attached heart monitors to deer and drove by them on an established snowmobile trail. The deer didn't usually run when the sled stayed on the established trail and didn't stop, but theie heart rate went up an surprising amount whenever a sled drove by, even though they didn't display any obvious response..
