If you live in a neighborhood with lots of trees, especially a crowded urban area, sunset and early evening can play weird tricks on your depth perception. Walking alone in the evening, as I do quite a lot around my neighborhood to the store (or more likely) bar, I try to keep a sharp eye on who's behind me and in front of me. It's not to say I'm paranoid, but after a friend of mine got jumped one night in my neighborhood walking back from "our" bar - her purse was stolen and person beaten by a group of guys - I try to be aware of what's going on around me. If you're starting out on a block corner and someone is at the other end, the streetlights can make the person at the other end of the block look bizarre.
The other night I saw this man and I swore he walking sideways doing a jig, the flecks of intermittent light acting almost like candlelight would. I thought well, not surprising but really that's too much cardio for this hour. The hardest part is being able to distinguish if someone is walking towards you or away from you. This is a good bit of info to have say, if I'm alone and a 6'2" man is at the other end of the block. I might cut over, just in case, so I don't have to treat a perfectly nice person as a psychopath or a psychopath as a friendly neighbor. The frustrating part of this streetlight, gettin'-jiggy, dancing phenomenon is the inability to tell which direction someone is going no matter how much you strain to look. I think that's been my month.