Dear RHH,
Thank you very much.
This certainly does seem the best supported and most likely of
the hypotheses. And, as I remember the expression on Twain's face,
it seems a bit more pained than amused. Of course, such an
expression could be used as part of a joke, but it is more likely to
indicate uncomfortable compliance with an undeniable request, exactly
the sort of response any of us might have to a sculptor who asked us
to get cold and uncomfortable for a while.
Viva!
FJH