Ninja cereal.

In the mid-1980's, Quaker Oats introduced Ninja Bites, which was basically just Cap'n Crunch in the shape of ninja swords and ninja stars.  They launched the product with a special promotion: free ninja stars.  If you bought a box of Ninja Bites, there would be brightly-colored plastic ninja star buried at the bottom of the box.  I remember getting my arm all sticky digging around in the box instead of waiting until more cereal was gone like my mom told me to.  I got a blue one.  It was a great promotion, except for one little detail: the promise that a handful of lucky eaters would find a real ninja star at the bottom of the box.  Four kids severed fingers digging their hands into the bottom of the box before they issued a massive recall of the brand.