LOL!! This morning the sun shone in the window and cast an odd shadow on the window shade. Because I hadn't finished my coffee, I didn't bother to check the window itself. I puzzled over it for a while, but decided there must be something outside that caused it.
Just went to the window to chase a bird off the air conditioner (trying to nest there). Pulled up the window shade. Last night, C took a baby wipe and stuck it to the window pane.