Если не подстригать когти, кошка снова будет царапать кресло.

Russian can use an infinitive in an если clause to make the condition sound general and impersonal.

So Если не подстригать когти... means something like:

• If you don’t trim the claws...
• If one doesn’t trim the claws...
• If the claws aren’t trimmed...

It is not tied to one specific person. It sounds like general advice or a general rule.

The subject is understood as a general person: you, one, people, or whoever is responsible for the cat.

Russian often leaves the doer unstated when it is obvious from context or when the statement is meant generally. In English we often supply you or people, but Russian does not need to.

This is an aspect question.

• подстригать = imperfective
• подстричь = perfective

The imperfective подстригать is used here because the sentence talks about a general, repeated situation: trimming claws as regular care.

So the idea is:

• If claws are not kept trimmed, the cat will scratch the chair again.

If you said Если не подстричь когти..., it would sound more like one specific occasion:

• If you don’t trim the claws this time, the cat will...

So both are possible in Russian, but they give different shades of meaning.

Because будет царапать is the future of the imperfective verb царапать, and it suggests repeated or ongoing behavior.

Here the idea is not one single completed scratch, but a repeated habit:

• the cat will go back to scratching the chair
• the cat will keep scratching it

Compare:

• будет царапать = will be scratching / will scratch repeatedly
• поцарапает = will scratch once, or will leave a completed scratch mark

In this sentence, the imperfective is more natural because the chair-scratching is presented as a recurring problem.

Снова means again.

Here it modifies the action будет царапать: the cat will again scratch the chair.

Russian word order is flexible, so you could also hear:

• кошка будет снова царапать кресло

The version in the sentence, кошка снова будет царапать кресло, is very natural and neutral.

Here когти is the accusative plural, which for inanimate nouns has the same form as the nominative plural.

Even though Russian sometimes uses the genitive after negation, the accusative is very common, especially when the object is concrete and specific. In this sentence, the claws are a definite set: the cat’s claws.

So:

• не подстригать когти = normal, natural
• не подстригать когтей = possible in some contexts, but more marked, less neutral here

A learner should usually treat не подстригать когти as the standard choice in this sentence.

It is in the accusative case, but for a neuter singular inanimate noun, the accusative looks exactly like the nominative.

So:

• nominative: кресло
• accusative: кресло

That is why the form does not visibly change, even though it is the direct object of царапать.

Because Если не подстригать когти is a subordinate clause, and кошка снова будет царапать кресло is the main clause.

In Russian, clauses introduced by если are normally separated by a comma.

So the structure is:

• Если ... , ...

This is true whether the if clause comes first or second.

Стричь is a general verb meaning to cut, to shear, or to clip.

Подстригать has the sense of trimming or cutting a little to keep neat. That is why it is especially natural for things like:

• hair
• nails
• claws

So for pet care, подстригать когти is the normal expression for trim the claws.

Russian often leaves possession unstated when it is obvious from context.

In this sentence, everyone understands that когти means the cat’s claws, because the next clause is about кошка scratching the chair.

If you wanted to make it explicit, Russian could say:

• Если не подстригать кошке когти...
• Если не подстригать ей когти...

But in the original sentence, that extra information is not necessary.

It can do either, depending on context.

Because Russian has no articles, кошка can mean:

• the cat
• a cat

In real use, this sentence most naturally sounds like a specific practical situation: someone has a cat, and if its claws are not trimmed, it will scratch the chair again.

But grammatically, without more context, Russian does not force one interpretation the way English articles often do.