Board Thread:Rewatching "Merlin" - Season One/@comment-5102537-20130214143847/@comment-5674726-20130407215220

He'd just woken from an enchanted sleep. His reflexes may have been sluggish.

ETA: I doubt that that point was considered, to be honest. The plot required Merlin to save the day so he could be rewarded with the position as Arthur's manservant, so Arthur didn't duck when the knife was thrown at him.