First off, this song kicks monster ***, but Funk generally does so it's not that surprsing

There's a glitch in the video about 2:15 in, it's a 2-second break. http://www.youtube.com/watch?v=dSC29xl6hno

This was from 1972, the same year the song was released, Stevie Wonder also performed it that year on Soul Train. They really jam with it on Sesame Street, running it nearly double the song's original length, kinda hard to believe they'd put it on Sesame Street, but it's not an inappropriate song in terms of lyrical content, so why not?