Shelagh Fogarty is Leading Britain's Conversation.
18 August 2016, 12:58
This is fantastic fun: David calls up James O'Brien with a Mystery Hour answer...that completely slips out of his mind as soon as he gets on air.
An earlier caller had posed the question: why do people have "upside down colanders" on their chimney? James said it was to prevent birds flying down and into the house.
David in Guildford seemed extremely confident as he joined James on air, telling the presenter he was "half right" with that answer.
But when James encouraged him to reveal all, David drew a total blank - and it left O'Brien in stitches.
When he recovered, David managed to get a round of applause for the answer: they're called cowls and they revolve in order to stop draughts getting into the house. Well done David!