Kelly inherited one of those free-standing room air filters from me a year or so ago when I bought a larger one for the den. Now it will occasionally go into a thrashing fit and wake her up -- I guess the bearings are going on the fan. I told Kelly that she'd have to live without a filter, since it was just an inherited hand-me-down anyway.
"I can't sleep without a fan now. 'Cause otherwise I lose sleep with the explanation cycle."
"What," I said, "is an explanation cycle?"
"Well, it's when I get woken up by a noise in the middle of the night, and I'm scared, and I have to think about what caused the noise, so I can go asleep. I can only go back to sleep when I've explained what made the noise."
So the explanation cycle is the list of likely causes for a nighttime noise she goes through until she finds a suitable explanation, and can go back to sleep. I'm going to add this to the Kelly lexicon.