Cirerita from another thread:
I have those ones as well. I think they're called slipper warmers or something like that. The idea is to keep your feet warm when it's really cold. They're useful if you're sitting down for a long time, believe me. Mine are USB, that is, you plug them into the USB port of your computer to get some extra warmth.
There are also glove warmers for your hands. If your wife keeps the heating too low, these warmers can save your life
They have Happy Dog ears. :)