Blind Sight

I noticed the other day that the window blinds in one room have taken to waving about on their own. We have lived here for six months, and it never happened before that the slats of the blind turned this way and that as though a hand were swiping them or, at the very least, as though there must be a gentle gust somewhere. I searched, and Spouse searched, for an open window- for any reason to explain the all-of-a-sudden change; but not a hint of explanation was to be found.
It started mysteriously and out of nowhere, and I am inclined to suppose it will finish up that way.
In that room I make my conversations with Mater courtesy of the telephone. Our communication has been improved significantly in recent times by the addition of a camera that enables us to see each other in our respective telephone positions.
"Do you have a window open?"
Mater was squinting at the grainy, moving image, staring beyond my shoulder at the big window illuminated with faint strands of afternoon sunshine.
"It's not open."
It being January, I rarely, these days, open the windows for long.
"It looks like it's open."
I could not think what she meant by her insistence. I told her so.
"Well, the blinds are moving about. I thought you had the window open."
I ought to have known. This is the very same Mater who, after Spouse and I visited an open house with a view to buying it, and later forwarded her the details, including pictures, responded by remarking, "I see the children of the house drew all over the walls."
I doubt if any of the foot traffic in the open house took note of the scribbles; but Mater observed it in a digitised, poor-quality copy of a copy of a copied photograph.
Maybe Mater, along with her eagle eyesight, has some suggestions as to just why the blinds sway the way they do.