Thanks to another Vi Hart video, this time I’ve learned all about flexagons. They are very fun to make; kind of like a cross between a Möbius strip and an origami fortune teller.

Woodcuts by by Bryan Nash Gill. Also available in book form.

I can verify that shadows can indeed accurately tell time, you just have to ask politely. I see no reason not to have one of these on every window— at the very least it would make me smile.

Sundial : How to make your own Cut Out Paper Vertical Sundial
[via Lifehacker]