It's Why I Married Her.

I couldn't find the handset for our landline today so, after a brief search, I phoned our number on my brick-like mobile (I asked for a downgrade, but that's another story). I could hear a muffled ringing out in the hall and found, to my amazement/exasperation/disgust, that it was inside 'er indoors' training shoe.
I tried to imagine the line of events that would lead her to do this but could not.