Computer mice, that is!
Here's the goofy story. I'm sure there's a perfectly logical explanation, I just don't know what it is.
The desktop computer I'm currently typing on has a Microsoft wireless mouse/keyboard combo. Some months ago -- perhaps as long as a year -- I started having some difficulty with the mouse. At first, it was just button clicks that didn't work the first time. Then they didn't work the first two or three times. Then cursor movement started getting flaky. Eventually a morning came when the cursor was just frozen in place.
I pulled out an old USB corded mouse and plugged it in. Since I was still using the wireless keyboard, which shared the receiver with the mouse (and which worked just fine), I now had two mice connected. I started using the corded mouse (despite frustration with my inability to get the buttons to switch; I mouse left handed) and all was at least semi-well. After a few minutes I accidentally bumped the wireless mouse, which was still sitting on the desk. The cursor moved. The buttons worked as well. Apparently I had shamed the wireless mouse into getting back to worse by plugging in the other one.
Since then I've been using the wireless mouse but have left the other one plugged in. Periodically the old symptoms start to reappear. I then grab the other mouse, move it around, click a thing or two, and the wireless one comes back to life. That's just happened in the last few minutes, inspiring this post.
So what's going on? Hardware? Software? Shame? The keyboard, by the way, has continued to work perfectly all along.