"They'd boil you down for bits to find out why and how you lived so long," Holmes says quietly.*
"About your cousin?" Holmes asks languidly. "Do please give him my warmest regards when next you see him." He gives Severus a small, knowing smile.
"And by all means, both of you, should you find any of my books in need of correction or emendation, feel free. I do not hold with the 'it must be true or they wouldn't have printed it' theory that seems to be so prevalent."
*Thinking here of Heinlein's Lazarus Long stories.