You know it, I know, everyone knows it. The pernicious enemy of all. You're walking one day and maybe you're in a bit of a hurry, and as you rush out, something snags at your foot; It's a wire.
"whew" you thought. You didn't trip over this time but next time there are no guarantees. It may not take in the form of a wire as seen here. It might be shoelaces or a branch, or who knows what form it'll take, but if you don't watch out, it'll trip ya, or trip something else over, and it won't be pretty.