Once King Tamzar got a hold of the Guard's Arm, he asked for the Guard to pull up his own sleeve. Getting a better grip of the Dagger, he uses the very tip of it just to drag it across the Guard's Arm. He didn't want to cause any strong deadly damage so he tried to be as careful as humanly possible with this light cut.
The Guard took the cut without even flinching, because he didn't want to appear weak and it didn't really hurt enough to howl in pain. But what test would King Tamzar need to do on a Guard, why a Guard? It would make anyone over analyze this situation especially since he cut his own kind. A revolutionary leader like King Tamzar wouldn't do something like this randomly, it is likely very thought out or it could be random! We never really know!
"Good. How many ores of this new type have the Miners found?" Asked King Tamzar as he let go of the Guard's Arm.