It's funny -- when I first heard the theme for May, I was intrigued, but considered sitting it out altogether because I wasn't sure I'd be able to come up with any ideas. Now I have more than I'll probably be able to do. I don't know if I'll be able to pull some of them off though, we'll see how the month goes.
Here's one idea I had using shadows for the 'creepy' factor:
Be sure to check out other creative interpretations of the 'On The Street' theme over at Self Portrait Challenge.