A native speaker reads a picture book to a kid. It goes like this:

Tip (a cat) is here. Tip is not sleeping. Who is sleeping? (A dog is sleeping)


(several pagers later)

Tip is here. Tip is sleeping. Good night, Tip.

The woman who reads the book stresses the word "IS" in the above sentences.

Would you please explain the reason to me?

Thanks a lot.


It's to indicate surprise or highlight a change in the situation.

Ah, finally, Tip is sleeping now.