Although the first American film serial was "What Happened to Mary", "The Adventures of Kathlyn" is a more important piece of film history, being the first serial to use cliffhangers as the ending of its chapters—and thus the first recognizable film serial. Frank Leon Smith, in a letter to "Films in Review" (February 1958), wrote that the cliffhanger ending of chapter one "was a 'situation' ending, but other episodes wound up with sensational action or stunts, broken for holdover suspense...gave the serial both the key to its success and the assurance of its doom."