The other night, Charlie shared a song with us he'd learned from a friend at school. I found many different versions on the web. The chorus Charlie does by saying a nasal "rah, rah, rah" that sounds kind of like scratching a record.
Here's a 
recording of Charlie and Daniel with the words below, so you can sing along.
Beaver one, beaver all let's all do the beaver call
Beaver two, beaver three lets all climb the beaver tree
Beaver four beaver five, lets all do the beaver jive
Beaver six, beaver seven lets all go to beaver heaven
Beaver eight, beaver nine... STOP! It's beaver time!
Go beaver, go beaver, go beaver beaver beaver!
Each chorus has a particular set of hand motions associated with it. It's pretty contagious.