That's Not a Dust Spot, It's a Balloon
Sometimes you're concentrating so much on the ostensible subject matter of a photo that you miss other elements altogether. Sometimes what you miss is a streetlight sprouting from the top of someone's head. Sometimes it's more interesting. I was going back through thumbnails of photos I took a few days ago, when it seemed to me that was a strange-looking dust spot at the top of the frame. Closer inspection showed it wasn't a dust spot at all, but a hot air balloon instead. I was so focused on the heron that I completely missed it when I snapped the shutter. Another reason it doesn't hurt to look back at old images with a fresh eye now and then.