I don't know what the Grimm might be feeling right now, but happiness is not one of those things; at the last second, it had understood everything, but it was too late.
The walls appeared like they did every hour; they changed exactly every hour, and there was a complex pattern in the place they would be appearing, it took a few hours, but I was able to solve that puzzle.
It is the reason why I changed my position the moment I sensed it and used everything I had, from words to my shield, to stay on the spot.
From my vast experience, I know how Grimms behave; this bastard behaved exactly as I had thought it would; it even maintained the same distance as I had expected, which made things easy.