"Fascinating" really is the right word to describe this deceptively good short story by Lydia Schoch. It's not often that I finish a story, short or long, and immediately go back to the beginning for another helping. Tumble managed to do that, and that by itself is notable.
It works so well because the story's tone is a very smooth, almost imperceptible escalation from banality, to healthy curiosity, to benign but notable strangeness, and onward through a few more levels that I won't spoil. That smoothness was a major factor that got me to go back right after I finished it; I was left wondering whether I had missed a hint or two or a page somewhere.