"Pop Goes the Weasel" is a traditional Nursery Rhyme and Song, which in some areas is sung as part of a children's game. The exact meaning of the song is obscure, but it is probable that it arose in the early days of Music Hall which was associated with pubs. A third verse of the song mentions "In and out the Eagle" where "The Eagle" referes to a certain London Pub. The melody is sometimes heard on TV, such as a jazzy version used in an early episode of "The Prisoner". The sheet music, Midi and Mp3 files for this song can be downloaded using the links in the left-hand menu.
The image below is the first page of the sheet music, and here you can download the full sheet music for Pop Goes the Weasel for piano in PDF format.