Nice! I like the notion of slivers too skinny to see — reminds me of when I was a (very skinny) kid, running around in the woods and constantly getting slivers in my finger. (Not too many barcodes back then, though.)
My first several drafts of the poem played with the notion of bars in an open cage of indefinite extent. That was a little more metaphysical than I wanted to get, but it is closest to the thought I had while walking.