Clackers, the popular late 1960s and early 1970s toy made of two hard acrylic balls attached to a string, became a global craze before being abruptly banned because their design turned out to be far more dangerous than manufacturers expected. The toy worked by swinging the balls up and down so they struck each other rhythmically, creating a loud clacking sound that made them addictive to master, but the repeated high impact collisions caused the acrylic spheres to weaken and sometimes shatter. W