From its start in 1969, “Sesame Street” has been closely tied to songs. “Music is a character in the show,” Louis Henry Mitchell, a creative director at Sesame Workshop, said. “It gives a rhythmic voice to what we’d be saying anyway.”

The 50th anniversary of the show has provided a moment to look back at its origins, its roll call of celebrity guests and how it shapes its songs, as well as one of its most viral musical moments: Feist giving a counting lesson to her hit “1234.” Here are nine more fluffy facts about “Sesame” sounds:

Ernie’s ‘Rubber Duckie’ is the only original ‘Sesame Street’ song to hit the Billboard charts

Sung by Jim Henson, it reached the Top 20 in 1970. (It was nominated for a Grammy, too, but lost .) Its success spawned many follow-ups and covers, notably a 1994 version by Little Richard, who appears to be playing his piano from a bathtub.

Written by Jeff Moss and arranged by the original “Sesame Street” music director Joe Raposo , Ernie’s paean to his bath-time pal is an earworm in the extreme. After she had children, Norah Jones suddenly found herself singing it. “I don’t even know where it came from,” she said. “It was just inside my bones, during bath time.” Nearly 50 years after its debut , it remains a “Sesame” staple. “We are always looking to find the right artist to do ‘Rubber Duckie,’” said Ben Lehmann, executive producer of the show.