Characters
You're like one of those Chatty Cathy dolls except I'm not pulling the string, you are. Blah! Blah! Blah!
— Neal ‧ Planes, Trains & Automobiles
Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker compares a nonstop talker to a talking doll, then adds a twist: no one is pulling the string here, so the chatter is entirely the other person's doing. The mocking 'Blah! Blah! Blah!' conveys exasperation at endless, self-propelled talk.
Context reviewed