If you joined us at today’s Harvard Chocolate Festival, then you might have seen us walking around with some mysterious white tubes. We challenged you to figure out how they worked — in case you didn’t get it, or want to make your own, here’s how they were put together! No matter which string you pull, it causes all of the other strings to shorten so that only one string is long. Here’s the secret: On the inside, the two strings are loosely looped together. It’s important to note that they’re not tied in any way. The same effect can be done by threading the two strings through a washer. The washer must be left free-floating and not secured to either string. There’s an excellent set of instructions available at this Berkeley site.