Looks like this manga will reward re-reads, with its foreshadowing in earlier chapters. I wonder if Tsubana-sensei picked up this foreshadowing device during her days as an assistant to Ishiguro Masakazu. He too is very fond of this sort of thing.
I also like the misdirection with the spider. It's the kind of thing you'd see in a Hollywood A-list flick, and further reinforces my feeling that Tsubana-sensei cares very much about her stories.