Without a doubt, that's a ghost. Seriously I've noticed the same problem here while it's raining or just about to rain. Love that door though although what's on the other side? Boo!
Dorothy Michaels: No, just Dorothy. Alan's always Alan, Tom's always Tom and John's always John. I have a name too. It's Dorothy, capital D-O-R-O-T-H-Y.
You might just have caught yourself a ghost here!
What is the structure?