Elliot was just singing “Rock A Bye Baby” to Bob (his lamby).  But instead of singing “bough”, he was singing “ball.” 
When I corrected him, he told me, “No, it’s ball.  When I was in your tummy I went to the Rock A Bye Baby song museum.  You opened your mouth and the sound waves went down your throat and into my ears.  That’s how I know the song – cuz I went to the song museum and heard it.”