Played in the movies by a female mule named Molly who was easy to handle. She was trained by Lester Hilton, who went on to train Bamboo Harvester aka Mister Ed.
Francis's voice in the films was provided first by Chill Wills and then in later films by Paul Frees.
Trainer Hilton used a technique whereby a thread was strung through the horses mouth that when tugged gave the impression that she was speaking. He used this same technique with Mister Ed.