One of my former students had a famous mother-in-law: the singer and entertainer Cilla Black. When I called round to see him and his father-in-law I asked after Cilla.

‘What kind of question is that?!’ said the father-in-law.

I had clearly offended him, but I had no idea how. Then I remembered that Cilla had died in 2015.

I assumed that Cilla’s widower had forgiven my faux pas when he offered to show me round the flat. He said that I could take a soak in the huge marble bath whenever I pleased.