Here's a fun trick: Take a short length of tube, with different markings on each end—these can be X and O, or colors, or whatever like—then spin the tube on a table. When the tube is spinning, if you look at it from above, you will see only one of the two markings. Sometimes it's one way, sometimes it's the other way. Hmm. That's odd.
In the video below, mathematician Tadashi Tokieda demonstrates this trick with a black-and-orange marked tube. He then walks us through the logic of the trick, going deep on the math behind it. Whether you care about the math or not, this is an interesting trick (and conversation-starter) to try with your friends. Enjoy: