Blaine's too busy staring at the sudden appearance of Toothless's teeth to really think too hard about the dragon's motivations or reasons for being out and about. He didn't know teeth could work like that, but unless he was just seeing things as a result of the late hour, clearly in this case, they could. But then any other thoughts are driven from his mind as he starts to back up while the dragon moves forward, slowly but surely.

As he backs up, he glances behind him to see if there's somewhere he can escape to. It's a slim chance because there's walls on every side, but if he moves quickly, he might be able to slip back into the entrance hall. His odds don't seem that great, but at least if he can make it there, he has a better chance of running away than he does in this hallway.