I'm not sure what you are referring to. Justin Kaplan in _Mr. Clemens and
Mark Twain_ quotes Clemens as saying about the death of Suzy: "It is one of
the mysteries of our nature that a man, all unprepared can receive a
thunder-stroke like that and live." However, Kaplan says that Clemens wrote
these words "nearly ten years" after Suzy died. The source Kaplan gives is
the Paine edition of the _Autobiography_, volume 2, page 34.