The paladin will not take poison damage in certain directions. When hit from a certain direction, and he proceeds to face that direction, he will block the poison damage. This isn't limited to only cardinal direction, but to diagonals too.
As such, if the paladin was hit from the top, and he turns and faces the top, he will block all poison damage from the shot that was hit by the top.
Edit: Changed from "Facing down", which was incorrect, to "facing towards where the projectile had hit".
