It is amazing what will burn itself into the retina of the mind. I have this vivid memory of a Sunday afternoon when I was about the age of 9 or 10. We heard the sound of an ice cream van round the corner as we often did and I was sent out to buy what was called "a family block" (no home freezers then). It must be in my mind as one of the first times I was sent on such an errand. Anyway having got the family block I was careful to thank the ice cream man very much, mainly because I was taught to do it that way, although it probably came over very sincerely. Anyway he said (I remember what he said not the man himself) trying to equal my politeness "Don't mention it". Now this wasn't a phrase I had come across before and I wasn't sure if I'd slipped up and said something I shouldn't. Anyway I pondered this all the way home and asked about it, if I recall correctly, and was reassured I had done nothing wrong.