NPR's Renee Montagne talks with literary sleuth Don Foster about his new book Author Unknown: on the Trail of Anonymous. Foster has made a name for himself by putting a name on works when their authors don't. He's been credited with discovering the author of Primary Colors, he discovered that a poem signed by W.S. was indeed a lost work of Shakespeare. recently, Foster believes, that Clement Clarke Moore did not write the classic the Night Before Christmas. Foster says it's actually the work of Major Henry Livingston, a veteran of the Revolutionary war, who penned the poem in 1823.