Meaning of "garn" in My Fair Lady?

Question

At the beginning of the My Fair Lady movie, there is a monologue of prof. Higgins like this: Hear a Yorkshireman, or worse Hear a Cornishman converse I'd rather hear a choir singing flat Chickens cackling in a barn Just like this one Garn! My question is: what is the meaning of this "Garn"?

Answer 1

It's Cockney for "Go on", basically meaning the same as "You're pulling my leg", i.e. "I don't believe you."