'What does it mean to have a w**k?' asks the ten-year-old carryingly as we enter a peaceful country tea room.
'It means to have a walk,' says my brother quickly. Our mother, reared in wartime Bristol when provincial slang was out of synch with modern pleasures, routinely suggests a nice little w**k after lunch.
'We can't let her think that,' I hiss, fearing the implications of our lengthy morning walks to school.
We both turn to the Vicar who is masticating placidly on a scone.
'It means,' he says, 'to, um, touch yourself...'
'We can't let her think that either,' I say, mindful of the ten-year-old's obsessive fiddling with her hair.
Luckily I recall a piece of intelligence passed on by a parishioner during casual conversation in the vicarage garden.
'We all,' I repeat doubtfully, 'have a 'happy spot'...'
'In our house it's the sofa,' says my brother.
The ten-year-old is looking bewildered. Worse, her young brother has left off his perusal of the cake stands and appears pruriently agog. I flounder. Occupants of the surrounding tables are sipping their tea in disconcerting silence and I'm sure the flagstoned floor is causing us to echo. Yet I am conscious of my resolve to answer all biological enquiries with factual frankness.
The ten-year-old is poised to probe further and just in time I remember the killer response that I always deploy in sticky situations: 'Wait till we get home,' I tell her, 'then Dad will explain it!'
How would you have enlightened your young daughter and an audience of elderly strangers?