It's fuzzy and imprecise, as many legal concepts are. Small/unoriginal enough snippets may not even be copyrightable:

https://en.wikipedia.org/wiki/Threshold_of_originality

Then even if it is copyrightable, under some circumstances your use of it may be considered fair use anyway:

https://en.wikipedia.org/wiki/Fair_use#U.S._fair_use_factors

Or potentially de minimis:

https://blogs.library.unt.edu/copyright/2017/09/05/the-de-mi...

But when in doubt, ask for permission or ask a lawyer.