- Mark Twain's Other Woman: The Hidden Story of His Final Years, Laura Skandera Trombley
(....sewing machines? -- One opportunity for ad copy was lost: Twain's secretary bought him an Arnold electric vibrator for massage, but first tried it out with her future husband: "We had a most lovely evening." Trombley comments wryly: "Twain loved his slightly used Arnold electric vibrator.....(and) subsequently purchased a second vibrator that ran on batteries.")
ETA: In her endnotes, the author links to this website with pictures of some truly terrifying Mark Twain memorabilia (that DOLL). But still, no sewing machines.