a grate fear

So, everytime I have to park near a drainage/sewer grate (which I frequently do in front of our house, and I had to at yoga tonight also) I think about what would happen if I dropped my keys and/or cell phone down the grate. Now, I never have (thankfully). So is this just acknowledging my clumsiness? or a manifestation of a paranoid or controlling tendency? and will thinking about it cause me actually someday to drop my keys down there?

I've seen enough movies etc where people crawl through the sewers, rats run rampant, etc -- plenty of images in our culture about the dark underbelly of the city. And hey, I read Les Miserables at a young impressionable age. (it's actually pretty exciting for preteens, all that filth and suspense). Maybe I can just blame my fear on 19thc literature. (hah!)

but really, is this just my own paranoid fear or do other people think about it too? I mean, I drop my keys probably once a week, somewhere -- at Starbucks, at my office door as I'm managing my armload of stuff, etc. Is the grate just waiting to get me?