I notice they're taking it easy with each other despite both missing accessories. Normal yukkuris would start by attacking each other.
BTW the convection would eventually heat the ribbons enough and set them on fire anyway. Given enough time. The problem is, those two managed to accomplish burning the accessories directly before that. Gotta give some easy credit to them for their stupidity. Not that they had choice other than to starve to death though.
I notice they're taking it easy with each other despite both missing accessories. Normal yukkuris would start by attacking each other.
Aside from the one where the Reimu attacked the Marisa when it took its hat off to use it as a boat, yukkuris normally recognize each other if they actually see the accessories being removed. The fact that they can still see the accessories might also be part of it.