I'm pretty sure I remember that from the Cub Scout book.
Albeit, the glass coating was a section towards the kite, and used to duel another kite, severing the other kite's string, rather than the throat of the other kite flier.
Or, anybody else, for that matter.
exactly, read a book called Kite Runner, its what they do, sort of like a race i guess... though i dont see how you could cut THREE peoples throats...