I heard this a while back, it's a little funnier:

http://www.npr.org/2013/02/22/172433807/misquoting-mark-twain

also, about 2 weeks ago there was another author on NPR talking about his
new book on misquotations; much of what he had to say was about MT.  Sorry
do not recall the name, maybe someone else heard that story...

ps:  In  Casablanca, Humphrey Bogart’s character never says “Play it again,
Sam.” Really. Look it up. What Rick really said is "If she can stand it, I
can. Play it." The latter may be correct, but the former sounds better to
our ears and therefore has been repeated in our society until it sounds
right.  Thus misquotations--or even full blown myths (George Washington to
father after chopping down a cherry tree: "I cannot tell a lie...").


-- 
Prof. Harold K. Bush
Professor of English
3800 Lindell
Saint Louis University
St. Louis, MO  63108
314-977-3616 (w); 314-771-6795 (h)
<www.slu.edu/x23809.xml>