Which is correct?
_______ the night before Christmas, when all through the house, not a creature was stirring, not even a mouse.
‘Twas is a contraction of it was, and the rule with contractions is that we use the apostrophe to stand in for missing letters.
For more holiday grammar fun, see my 10-question quiz: ‘Tis (or t’is?) the season. I bet you’ll get the title question correct, at the very least.
How Stuff Works includes A Visit From Saint Nicholas in its list of the top ten myths of Christmas. Apparently, although Clement Moore is usually credited as the author, he probably was not.
Follow me on Twitter @tao_of_grammar