If you like river crossing puzzles, you'll love this video. In a slight twist on the "cross the river with these annoying restrictions" formula, this TED-Ed lesson has you escaping zombies across a rickety bridge. With a few tries, you may be able to solve this...or you can just let the solution be explained to you. (Note: there is no "trick" or way-outside-the-box thinking; you just have to think through the different timing scenarios.)

For more on this, check out the TED-Ed lesson page.