in the dark, bright light destroys your ability to see in the direction the light is coming from, so it causes disorientation. deer and rabbits and other nervous animals this causes shock, their blood pressure drops because their pulse weakens. cows are quite nervous animals too, but not as nervous as rabbits or deer, and animals like cats and sheep and goats (and weasels and raccoons) are just crazy so when they get that shock reaction their adrenalin surges and they run. humans are somewhere in between.