At breakfast one morning last week my husband put forward the following hypothesis: the reason he has had so many colds this year is that he keeps losing his scarf.

I told him not to speak in this way in front of the children; the thought that their malleable minds should be exposed to such unscientific tosh was painful to me. It is a proven fact, I said, that one does not get a cold because one is not wearing a scarf. It is a proven fact, he replied, that one does.