Hand-held toys known as “fidget spinners” – marketed as “stress relievers” – have become so popular and distracting in classrooms that they are now being banned in many schools. And it’s not just kids who like to fidget. Look around your office and you will probably see people bouncing their legs up and down, turning pens over and over in their hands, chewing on things, sucking on their lower lips and pulling bits of their beard out – seemingly completely unconsciously.