His teenage kid asked him what "defenestration" meant, and rather than giving a succinct answer his interest in history took over and before he knew what he was

His teenage kid asked him what "defenestration" meant, and rather than giving a succinct answer his interest in history took over and before he knew what he was doing he'd started giving a mini-lecture that involved the defenestrations of Prague, only to snap out of it when he realised people were so uninterested that they'd got up from the table and were doing other things.