They can hear but how they react is a mystery. A few weeks back while rattling with another guy I was watching a young buck come cautiously in looking for the fight, unknown to me the other guy was eyeing up another buck coming in from the backdoor when he shot the young buck & I jumped out of our skin(we were about 100-150 yards apart). That sucker hit the ground running and was out of there. On the flip side I have seen deer just stand their and yet others run directly toward the shots fired. One theory I have is the sound bouncing back caused deer to think the noise came from the rear not the front and start to run toward the shooter on the flip side when they stand there they heard the shot but just are not sure where it is and just hang tight for a moment or two. Distance shots I have seen them pick up their heads and others just keep about the business like nothing had happened. Again just another mystery of deer hunting why they chose to react or not is only known by that deer at that time, but you' ll never convince me they can' t hear a gun shot.