Nyota is right.
The part marked in blue is called an idiom:
What is an idiom?
An idiom is a group of words which, when used together, has a different meaning from the one which the individual words have.
- How do you know about John's illness?
- Oh, I heard it on the grapevine.
Of course, the second speaker does not mean he heard the news about John by putting his ear to a grapevine! He is conveying the idea of information spreading around a widespread network, visually similar to a grapevine.
We use idioms to express something that other words do not express as clearly or as cleverly. We often use an image or symbol to describe something as clearly as possible and thus make our point as effectively as possible. For example, "in a nutshell" suggests the idea of having all the information contained within very few words. Idioms tend to be informal and are best used in spoken rather than written English.
I'm not a teacher.