I think Mark Twain got even more annoying on the blu ray set. I was watching the episodes tonight and I was even wondering why did they include Clemens anyway?
Because Samuel Clemens aka Mark Twain was the first author to write a story about travelling back in time
, even though he mostly used it as a vehicle of satire to criticize the romantic notions people in the 19th Century had about the Medieval Ages.
And, of course, it's not without (self-) irony. Clemens suggested it would be possible to change the past while "Time's Arrow" explicitly states that you can't or won't.