On a train trip to London from the North some years  ago I sat at the same table seat as a  sweet, pink-marshmallow faced nun. (Always look for nuns and babies  to sit next to on trains and planes, in the sure and certain  hope that God will create a security bubble in their immediate vicinity in the event of a crash).  She told me the trip was her first time out of the convent in 15 years.  When she opened her little pack of sandwiches she squealed with delight, and said, Would you believe it.  Sister has packed the same sort of sandwiches as I had last time - lettuce and cress!  I said, How extraordinary.

A short time after finishing her lunch she got up, and said she was going for a walk through the train so that she would be able to tell the other sisters at her destination convent one or two more  funny stories (?).

When she got back, about 20 minutes later she looked rather worried.  I said, Is anything the matter, sister?  She said, Did I tell you I had lettuce and cress sandwiches the last time I went to London.  I said, Yes.  She said, I thought I did -  I'm awfully sorry.  While I was walking through the train it suddenly occurred to me that the sandwiches last time  were lettuce and cucumber.  I thought I would finish my walk, rather than coming back immediately to tell you. The sandwiches not being the same means one less story to tell the sisters this evening. Conversation will be quite difficult.