Hints:

We must be climbing a great big mountain!
It could be just a hill, you never know.
I'II know. I'II call it Sky Mountain.
Because that's how high it goes.
We're as high up in the sky as the birds.
You could be right. Look!
I can see the top!
I'll race you. Okay.
The top of Sky Mountain.
No, the top of Pudding Hill.
I thought this was Sky Mountain.
You can call it Sky Mountain if you want to.
Really?
But Pudding Hill is nice too.