A slightly different version of the song was part of this episode's video letter.
A kid throws a toothbrush out of the letter at the end. Joe picks up the toothbrush which had a clue (the third one) on it.
This was the second time an item came out from the video letter (the 1st was a popsicle stick [the second clue] from "Blue's Surprise at Two O'Clock!" and the third would be a stamp from "Our Neighborhood Festival"), the 2nd time a clue came from there (a clue [the second; a stage] would be found in a video letter again in "Joe's Clues"), and the only time the 3rd clue was found this way.
After Joe drew the third clue in his thinking chair, he realized he was already sitting in the thinking chair.