I don't know quite how to describe this but I'll give it a go. We were getting a burst of Jingle Bells several times a day and as Christmas is long gone, I thought I would try Bea's method, every time he whistled Jingle Bells, I whistled the "charge" whistle. So now we have.....Do, do , do do all the way!!! He's doing a little bit of the charge whistle and adding the end of Jingle Bells to it.