Sherreebonn & blubble blubble (Billy Connolly)

reading about panto and Billy Connolly I came across the word 'sherreebonn' (scots slang I presume) and a sketch which a punch line that scapes me.

I wonder if anyone familiar with Billy Connolly can help with this punchline, specially if you have seen it, as regard

1) where was he putting his head and
2) meaning of blubble blubble (is it a corruption of some word or phrase?)

the sketch mentioned is is the American Express one, which ended with the punchline "put your head in between them and go blubble, blubble, blubble with American Express".

thanks

Well. There's an expression in the U.S. that in case of nuclear attack: Put your head between your legs and kiss your a** goodbye. That was by way of illustrating the futility of civil defense drills.