This is the longest-running holiday ad for Hershey's, and it came about by pure luck. John Dunn was the creative who traveled to the production, and while they shot and animated other ads he asked if the production company could do this idea that he had just thought of. John also added the extra whimsy, as the bell that frantically rings at the end, wipes its brow with the plume and says "phew".
Ad agency: Ogilvy Mather
Creative Director: David Apicella
Brand manager: John Dunn
Production company: Colossal Pictures, San Francisco
Director: Carl Willat
Animator: Gordon Clark
Below - different end font and lines.