My (ex-?) dog, Major, doesn't live here anymore. But when he did, he'd run through the house, jump up onto my office couch, and slam into the window to stop himself. (Then he'd just nap up there in the sun, surveying the yard, waiting to go chase away cats or squirrels.)
So when he lived here I only ever opened the windows down because I was so horrified of the thought of him running into the office, jumping up atop the couch, and slamming into the non-existent window and plunging to his death (or cripplement) onto the back porch.
To this day I'm still paranoid of opening the window in the wrong direction and only ever open them down. But because the sun was hitting me and I wanted to lower the blinds halfway and still have the wind come through the house, I opened the windows up just now... and I keep looking over at it, paranoid as hell for no reason. Weird.