i believe most deer duck because of the sudden movement of a bow going off...i try to shoot deer when they are lookin away or when they cant see me with their peripheral vision...call me crazy but my theory is if sound travels at 300 fps and a bow is shootin that or better, then at 20 yards the arrow will hit the deer before it hears it...jus aim at the heart-that way if he ducks you still have a double lung and if he doesnt duck you get a perfect heart shot