That's a mechanic I haven't thought of much since early on in the story with leana... If any on the sky city residents have enough weight blown off of them, they'll automatically float back to their island. So mcgarrick didn't have the chance to kill hazan because he floated back to Ariadne...
Per Ch. 76, pg. 9 we know that a snake is a symbol of being wary of the unknown, at least. And if kittens are similar to lions, they represent Caligula's desire to protect Lulu and Noish.
I like that what he saw was a wall on the mural. It could actually have been an image of a wall - he's been trying to improve his power all this time and was reaching his limits. So it was a rather clever coincidence.