Reflex

Merlin dodged the sword strike, then brought up the shield to block another blow.
"Sire? Do we... always have to... train like this?"
"Of course Merlin. Being in a fight means you have to react instinctively... reflexively."
Merlin dodged the next blow, and Arthur sighed.
"Okay, we'll call it a day. At least you aren't as useless as before..."
He went to pat Merlin on the back, but the young man span around, and lashed out with his fist, sending the king to the floor with a bleeding nose.
Merlin hid the grin that was forming.
"Sorry Sire... Reflex."