You've probably seen some greying crocheted yarn around a telephone pole, or a tree trunk that looks like it's wearing a giant leg warmer. That's yarn bombing (or yarn storming) a form of graffiti that involves covering objects in public spaces with knitted, woven, or crocheted yarn cozies. It has gained popularity over the last 10 years. Some yarn bombers have gotten even more ambitious than trees and telephone poles. Here are a few of the most beautiful and outrageous examples of yarn bombing.