It's a shame that the very thing that makes a toy attractive is the one thing you can't advertise: the danger factor. If the makers of lawn darts had been allowed to write on the packaging, "The toy that could kill you if you use it wrong!" then nearly every kid in the world would be begging for a set. So it was with the simple, seemingly harmless 70's toy called Click Clacks (or, depending on where you grew up, Knockers, Knocker Bockers, Clackers, Ka-Bangers, Knicker Knackers, etc.). Had they worked only as the toymakers intended-as a noisy little twist on paddleball games-then Click Clacks might now be collecting dust in the Hall of Forgotten Toys. But no, these little spheres had a grander destiny: the much cooler Hall of Dangerous Toys.

The Click Clack design was like the answer to a Zen riddle: two orbs attached by a common string. By holding the middle of the string and moving their hands in a constant up-and-down motion, kids caused the thick glass spheres to collide at the top and bottom. Aside from looking great (especially if the balls were speckled inside with glitter), the toy made a highly satisfying clacking noise that you controlled. Many a parent was driven to profanity by this hellish metronome, but that was only the start of the Click Clacks' problems.

If you don't know the story, right now you're probably thinking, "pinched fingers." And you're halfway right. Those spheres could deliver a mighty whack to the untrained hand. But that was totally your own fault for being such a lame-oid with your Click Clacks, doofus. The real danger was a hidden one, at least until you managed to smack your Click Clacks together long enough and hard enough. When that critical breaking point was reached, those thick glass balls would shatter, sending Click Clack shrapnel flying. Usually, the spheres were chipped away a little at a time, but if you were on the wrong end of a surprise shattering, boy, were you in for a dandy treat.

Not surprisingly, just when Click Clacks got interesting, they were taken away. The toy went out of production, moving forever into the realm of schoolyard rumor and urban legend. Click Clacks did make a comeback in later decades in a safer (boringer) form, but the days of explosive, noisy fun were gone forever.