Kronos Quartet is a string ensemble established in the 1970s with dozens of recordings released to date. When they appeared on Sesame Street in 1987, the members of the quartet consisted of David Harrington, John Sherba, Hank Dutt, and Joan Jeanrenaud.
In one segment, Big Bird meets the players in the Arbor. The explain to Big Bird how a string quartet works and how it's something like how they're communicating. In another segment, the players are kicking around a soccer ball with Big Bird. They show him how passing the ball to one another is something like how they practice playing music.
David Harrington commented in 2012:
“"I'll tell you a secret about that. I promised my kids that I would come back with two of Big Bird's feathers. Let's put it this way: I found one lying on the floor, and the other one – well, I had to pluck it.”