When Darius reopened his eyes, he was unsurprised to see Marasmus' bony finger still pointed at him. It meant that only a few seconds should have passed since the Stonekeeper had shot the black light into his forehead.
During this short amount of time, Gunner had obviously been startled and worried, yet had stayed where he was.
It was mostly due to the fact that he had been unable to detect any malice from Marasmus, or he'd have charged in to protect Darius by any means necessary regardless of whatever prior orders he had received!
When his master woke up again, both Gunner and Marasmus observed him with curiosity. His Branded Servant because he was wondering what had happened to him, and the Stonekeeper because he looking forward to seeing Darius' reaction to having his question answered in this particular way.