I think I commented when Jirou Sugiura was drawing the rough version of this chapter and posting to his Twitter (and then Pixiv) something like half a year ago but Mamoru would have to have something like supersonic speed to be able to hear that the kid is falling, jump out of the window, run across the yard, and catch that kid who is only falling from one storey higher than the window that he jumped out of. It's still a good chapter despite the questionable physics.
Ambergris (oil from the intestine of a sperm whale that was used to make perfumes) is a very unusual scent for an eraser.