I had assumed the problem was the cats, since in a household with multiple cats, mysterious problems are very easily placed on the cats' shoulders. They won't complain and they often have some connection to the matter. In any case, the problem turned up when I was doing my step aerobics, on an elevated WiiFit Balance Board, in front of the television, and problem was some kind of grit underneath. I was stepping on something: not just a little something but a lot of small, fine particles that didn't quite dig into my feet, particularly as I was wearing socks, but which were steadily annoying anyway.
I figured the problem was catnip. My parents like to treat the cats to a whole lot of catnip all at once, since it does wonders at cleaning any sulking they might be doing. It won't surprise you that my father --- who, when he spackles a room ahead of painting it, routinely applies so much that the dimensions of the room are noticeably reduced --- applies catnip like he's hoping to melt the carpet. I swept off the balance board mid-step and was irritated to find I was still picking up grit.
However, further examination proved the cats were innocent in this regard. What had happened was one of my five-pound ankle-weights had ripped open, and the extremely fine ball bearings inside were leaking out. I knew I wasn't buying the highest-quality fitness gear, and I know 60 to 90 minutes of step aerobics a day curled around my ankles can be a bit much, but I didn't expect to rupture an ankle weight. I did discover where the vacuum cleaner was kept, so I know it'll never be kept there again, either.
Trivia: In 1920 the United States exported a record high $250,000 of pencils to Argentina, about ten times the pre-war rate. In 1921 it exported $75,000, and in 1922 less than half that. Source: The Pencil: A History Of Design And Circumstance, Henry Petroski.
Currently Reading: The Illustrated History Of Canada, Editor Craig Brown.