Writhing is a snake- or worm-like movement — a rolling and twisting motion, like your writhing brother who can't stand to have his feet tickled.
When you picture a wreath, you probably think of a festive decoration hanging on someone's front door. So it might surprise you that this word shares its origin with writhing, a word that often describes a reaction to pain or extreme discomfort. The wreathes of today are rings — originally, a wreath was a bandage that wrapped around and around. Writhing is also a rolling, or circular motion.