Eric: Interesting... I recently experienced a similar event. I shot a doe a couple of weeks ago. I used my single shot 12ga shotgun. She walked right to left and eventually stood broadside at about 70 yards; I put the crosshairs at the front (her left side) shoulder area and fired. The deer collapsed immediately to the ground, which I found rather strange considering my shot placement. I thought that maybe my shot went high and spined her or went left and hit her in the neck. When I retrieved the doe, I was surprised to see the neither. The slug entered her forehead straight on and exited behind her right eye.
I don't recall her turning to face me at the last second before squeezing the trigger. The shot was not rushed, I was calm and steady. It somewhat disbelief, I reasoned that she turned her head/neck to face the direction of the sound of the shot, when then the slug met up with her forehead. Considering the velocity of my cheap 12ga ammo, (1600 feet per second), I calculated the time it took for the slug to reach her which is .131 seconds. If reaction time of .02 seconds is true, that would support my assumption.
As I write this however, I'm diving deeper into the science of it. The speed of sound travels at 1125 feet per second (slower than the slug). The slug would have met her before hearing the sound. Even at 70 yards, the typical slug velocity slows to about 1300 fps. Still quicker than the speed of sound. So mathematically, she could not have heard the shot prior to the slug reaching her.
Still believing that she knew it was coming, the final thought that I have is that she saw the shot. I shot her just before dark; still shootable (legal) light but dark enough to "see" a muzzle flash. Considering the speed of light at 983,000,000 fps, the light emitted from the flash would have reached her in .0000002 seconds. So, maybe she saw rather than heard the shot...
Hard to believe. Maybe she just turned, unnoticed by me. Would have been nice to have it on video.
