"Aha. Thank you for telling me that."
One might think that Ernie is deliberately messing with Bert here, and that is a valid interpretation, but on the other hand, sometimes people just honestly don't realize how annoying they can be. I've encountered people like that and, in retrospect, I've realized that about myself at times. That ambiguity is one of the things that gives Ernie's character complexity.
Bert's book is called Bonfire of the Oatmeal, and it has a pigeon on the cover. It must have been written by a spirit kindred to his.
It's hilarious to me that Ernie says he's going to listen to some "rock'n'roll music". Maybe later they can go out for a hamburger sandwich and some french-fried potatoes!
This is Steve Whitmire performing Ernie and, as someone on the Muppet Mindset once pointed out, Ernie's doglike barking sounds a lot like Sprocket, appropriately enough. And yet, we also know from Fraggle Rock that Steve is capable of doing a much more convincing fire engine siren than he does here, so I must confess myself a little disappointed.