Plural or singular verb when plural subject is separated by an "and"? [duplicate]

A similar question is here, in which a comma is used in place of a conjunction like and.

I came across the following quotation of C. S. Lewis which reads,

“What you see and what you hear depends a great deal on where you are standing. It also depends on what sort of person you are.”

Assuming the website which quoted Lewis did not misquote him, should Lewis have used the plural verb, depend? Or is there some arcane rule of grammar of which I am unaware which allows for a plural subject and a singular verb?

Solution 1:

“What you see and what you hear” is treated as singular, not plural here, as you can see from the use of the word “it” instead of “they” at the start of the following sentence. Therefore, there is no plural subject.