Or tune as it were. I've been listening to Lindisfarne's Dingly Dell that has the live version of "We Can Swing Together" on it with the extended harmonica solo.

At one point a certain folk-sounding tune is played on the harmonica and then stops, wherein the band sings "OHHHHHHHHHHHHHHHHHHHHHHHHHHHH," the point seeming to be to hold the note as long as possible. All the people in the crowd seem to know it as very common and sing along, as the only other tunes they sing along to are "Jingle Bells" and "Camptown Races".

Any ideas?