At a pretty seaside town on the Basque coast. Pietro decides to go for a swim in the harbour. Choppy water. Changes into swimming trunks. Poised to jump in. Still wearing glasses.
G: You can’t wear your glasses. They’ll come off and you’ll lose them.
P: No they won’t.
G: Yes they will.
P: No they won’t.
Pietro jumps in. Two minutes later he gets out.
G: Where are your glasses?
P: I’m wearing them.
G: No you’re not.
P: Where are they then?
G: Perhaps they came off and you lost them?
P: Oh dear, yes, that must be it.
G: Groan [Not sure whether to laugh or cry.]
Glasses remain in the sea, lost forever.
And there you have it.