Some things in life are a complete mystery. Take, for example, this spot that has suddenly appeared on my kitchen floor. What precisely is it? I'm not sure. Any number of sticky things, I suppose.
The real question, however, is How did it happen to take the exact form of a question mark? That, folks, is the million dollar question! Unfortunately, the world may never know. It seems that our mystery stain has a pending date -- with my mop.