Watch someone burn themselves on a hot pan, struggle to lift heavy weights, or strain to hoist his leg up over his head and you'll probably notice his writhed lips — twisted in pain.
Writhed comes from the Old English writhan, meaning "make into coils" which is much like what you're doing when contorting yourself or putting yourself in a writhed position. The word writhed is used not just to describe an action but also to describe the quality of people or things. So while a snake writhes on the ground, its writhed body can also lie in a coil in the grass.