The other day I dropped something off my desk, which is something that happens from time to time. It rolled behind me, and my first thought was "I should make sure that didn't fall down into the heating vent." This was immediately followed by the thought, "What heating vent?", which left me so confused that I didn't actually pick up whatever it was that fell.
Our current house has hot water baseboard heat. There are no heating vents, just baseboard heating elements around the exterior walls of each room. The fact that this house has baseboard heat is one of the reasons we bought it: I think hot water baseboard heat is an entirely superior heating methodology, compared to central forced air heat. We've lived here now over two years, so you'd think I'd be used to it by now. So where'd the idea of something falling into the vent come from, you ask?
Simple. Behind me at my desk is a buffet cabinet that, at our old house, used to sit over the main return vent for the first floor. The grate over that vent was less than fully adequate, and things did routinely fall through it and into the vent. We lived there for six years, and I guess on some level my mind associates that buffet cabinet with the concept of a heating vent.
It took me a while to figure out where I was getting such a bizarre thought from. It's strange how the mind works. (Or maybe it's just me.)