Learn Russian: В лесу ни шороха. - There is not a rustle in the forest.

Using ни creates an emphatic existential negation. While В лесу нет шороха simply states a fact ("There is no rustle in the forest"), using ни translates more closely to "There is absolutely no rustling" or "Not a single rustle."

Why is the noun шороха in the genitive case?

In this specific verbless construction, the particle ни demands the genitive case for the thing that is absent. Because the sentence expresses a total lack of any rustle (шорох), it takes the genitive ending to become шороха.

Where is the verb in this sentence?

It is intentionally omitted. Russian frequently drops the verb "to be" in the present tense, but this specific emphatic structure (ни + Genitive) relies on being completely verbless to make the total absence of something feel punchy, absolute, and dramatic.

Why does лес become лесу here instead of the regular prepositional form лесе?

Лес (forest) is one of a handful of short, masculine nouns that has a special "locative" case when denoting a physical location with the prepositions в or на. Instead of the standard prepositional -е ending, it takes a stressed -у, making it в лесу.