poliphilo | Darkness Visible

I can't account for the shadow that appeared in the corner of our bedroom the night before last. It was triangular, pitchy black- and didn't appear to be related to any existing light source. Normally that corner of the room is dimly lit by reflections from street lamps and the shadows are clear- like brown consomme- and you can see to the bottom of them. This shadow was impenetrable.

I wasn't scared, The thing didn't seem sinister. Eventually it went away. I wish now I'd got up and investigated it but I was just too comfortable in bed...

Was it a portal? Was someone observing us who didn't want to be observed? Or is there some laughably mundane explanation?