This was a new one to me - see the little dots on the window? They are a reflection of the bigger dots - and they shouldn't be there.
Generally my Mac has been a wonderful tool, but occasionally I gotta reboot. No computer is perfect - not even a Mac.
By the way, I have been a Mac user since 1995. I had a two year blight in that during my 2 years in Kenya; my day job required me to use a Windows box. But even then, my home computer was a Mac.
Heather is a firm Windows person. It keeps our life interesting.