فراء القطة وشواربها نظيفان.

Because this is a present-tense nominal sentence in Arabic. In Modern Standard Arabic, the verb to be is usually omitted in the present tense.

So:

• فراء القطة وشواربها نظيفان
• literally: the cat's fur and its whiskers clean
• natural English: The cat's fur and its whiskers are clean

If you wanted the past or future, Arabic would normally use a form of كان:

• كانا نظيفين = they were clean
• سيكونان نظيفين = they will be clean

This is an iḍāfa construction, often called a possession or of construction.

• فراء = fur
• القطة = the cat

Together, فراء القطة literally means the fur of the cat, which English usually expresses as the cat's fur.

A key point:

• the first noun in an iḍāfa usually does not take ال
• the whole phrase can still be definite because the second noun is definite

So فراء القطة is definite and means the cat's fur, not just cat fur in a vague sense.

ها is an attached pronoun meaning her or its.

So:

• شوارب = whiskers
• شواربها = her whiskers / its whiskers

It refers back to القطة.

Why ها? Because القطة is grammatically feminine. In English, we often say its for an animal, but Arabic uses the feminine pronoun here because the noun قطة is feminine.

Because نظيفان is agreeing with the two coordinated subject parts:

1. فراء القطة
2. شواربها

Arabic is treating these as two things being described together:

• the fur
• the whiskers

So the predicate is dual: نظيفان = clean for two items.

In other words, the dual here does not mean there are only two whiskers. It means the sentence has two coordinated subject phrases.

Because the agreement here is not with القطة alone. It is with the whole pair:

• فراء القطة
• شواربها

Since the two parts are not both straightforward feminine singular nouns, Arabic uses the masculine dual as the default agreement form in this kind of mixed situation.

Also, فراء is masculine.

A useful comparison:

• شواربها نظيفة = its whiskers are clean
  Here شوارب is a non-human plural, so Arabic often uses feminine singular agreement.

But in your sentence, the speaker is describing two coordinated things together, so نظيفان is used.

Because here نظيفان is functioning as the predicate of the sentence, not as an adjective inside the noun phrase.

Arabic often distinguishes these two uses by context and definiteness:

• predicate adjective: usually indefinite
• attributive adjective: must match the noun in definiteness

Here, فراء القطة وشواربها is a definite subject, and نظيفان comes after it as the thing being said about it: are clean.

If you wanted something more like the cat's clean fur and its clean whiskers, Arabic would usually phrase that differently, for example by giving each noun its own adjective.

Yes, that is a very common question.

The singular شارب often means moustache, and the plural شوارب can also be used for an animal's whiskers. Context tells you which meaning is intended.

With القطة, the intended meaning is clearly whiskers, not a human-style moustache.

Because و meaning and is a clitic in Arabic. It is written attached to the following word, not separated by a space.

So:

• وشواربها = و + شواربها
• meaning: and its whiskers

This is normal Arabic spelling.

It is a nominal sentence.

The basic structure is:

• subject: فراء القطة وشواربها
• predicate: نظيفان

So the sentence is built like:

• [the cat's fur and its whiskers] [clean]

which English turns into:

• The cat's fur and its whiskers are clean

This is one of the most common sentence patterns in Arabic.