Chewing glass!

What is it about stuff on the floor that looks so appealing and desirable to kids!!  I heard Joshi crunching on something the other night, at first it sounded like he was grinding his teeth, then I realized he was chewing something, so I asked him what he was chewing on.  The look of complete and utter guilt that washed over his face was of course the main indicator that he was not chewing on a nice healthy snack!  "Spit it out", I said!  His jaws clamped shut knowing that he was on the road to being in deep diddles!  "Spit it out now Joshua Scott Lee"!  I held out my cupped hand by his mouth and lo and behold, he spits out a piece of glass that he picked up from the floor!  "Why" I ask, "why would you pick up something off of the floor and put it in your mouth, (never mind the fact that it's a piece of freaking glass), that is sooooooooooooo disgusting"!  So then I just get the glassy stare, you know that 'I know I did wrong but there are no words to explain my stupidity right now so I'll just stare at you", kind of stare!  What can I do with that?  My repeated question of "why" draws no logical answer, so I put him in time out for putting stuff from the floor in his mouth.  Did that punishment work?  Absolutely not!  Yesterday I caught him chewing on a piece of fluff, yes I said it, fluff, that he had, yes you guessed it, picked up from the floor!!!!!  Whyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy people, why?