There was a boyishness about Mr. Clemens sometimes that found different modes of expression.  Once, when the long corridor of the second floor of the hotel presented a temptingly empty avenue, he hopped, skipped, and ran, and then gave a delicious suggestion of a cake-walk.  As soon as a door opened, however, he stopped and assumed a supernaturally grave aspect.  ~Elizabeth Wallace, Mark Twain and the Happy Island, 1914