У кота їжа в роті.

Because after у in the phrase у кота, Ukrainian uses the genitive case.

• кіт = cat in the dictionary form
• кота = of the cat / used after certain prepositions and in possession patterns

In this sentence, у кота literally looks like at the cat or by the cat, but it is a very common Ukrainian way to express possession:

• У кота їжа = The cat has food

So кота is there because the grammar requires the genitive, not because the meaning changes to a different cat.

Literally, у кота means something like at the cat or by the cat.

But in normal Ukrainian, this structure often means someone has something:

• У мене є книга = I have a book
• У кота їжа = The cat has food

So in your sentence, У кота їжа в роті, the idea is:

• The cat has food in its mouth

A very literal breakdown would be:

• У кота = at the cat / the cat has
• їжа = food
• в роті = in the mouth

Ukrainian often omits the present tense of to be.

So where English says:

• The food is in the mouth
• The cat has food

Ukrainian can simply say:

• Їжа в роті
• У кота їжа

The meaning is understood from the structure.

In more formal or emphasized sentences, you may sometimes see є, especially for there is / there are or have-type meanings:

• У кота є їжа = The cat has food

But in many everyday sentences, especially simple ones, є is left out.

In many cases, у and в are just two forms of the same preposition. Ukrainian switches between them mostly for ease of pronunciation and smooth sound.

So:

• у кота
• в роті

This combination sounds natural and flows well.

Very often, у and в can both mean in, at, or by, depending on context. The choice is frequently about euphony rather than a big difference in meaning.

For example, you may hear both:

• у роті
• в роті

Both can mean in the mouth, though one may sound better in a given sentence.

Because after в when you mean in a location, Ukrainian uses the locative case.

• рот = mouth (dictionary form)
• в роті = in the mouth

So:

• в рот would usually suggest movement into the mouth
• в роті describes location in the mouth

Compare:

• Їжа в роті = The food is in the mouth
• Покласти їжу в рот = to put food into the mouth

That is the same kind of difference as English in vs into, though Ukrainian shows it partly through case.

Їжа is in the nominative case.

That is because it is the main noun of the sentence — the thing being talked about:

• їжа = food

Even though English might translate the whole sentence as The cat has food in its mouth, Ukrainian is not using a direct verb has here. Instead, the structure is more like:

• At the cat, food is in the mouth

So їжа stays nominative as the main subject-like element.

It can naturally be understood as The cat has food in its mouth, and that is probably the most natural English translation in many contexts.

But structurally, Ukrainian is somewhat close to:

• There is food at the cat, in the mouth
• or Food is in the cat's mouth

So the sentence focuses on the situation, not necessarily on a strong distinction between has and there is.

A more directly possessive version in English is usually the best translation:

• The cat has food in its mouth

Yes. Ukrainian word order is fairly flexible, and changing it can change the focus or emphasis.

Your sentence:

• У кота їжа в роті.

Possible alternatives include:

• Їжа у кота в роті.
• В роті у кота їжа.

These all point to roughly the same basic situation, but they sound different in emphasis.

• У кота їжа в роті sounds neutral and natural.
• В роті у кота їжа puts more attention on in the mouth.
• Їжа у кота в роті puts more attention on food.

So yes, word order can move around, but the original version is a good normal one.

Ukrainian does not have articles like English a and the.

So:

• кіт can mean a cat or the cat
• їжа can mean food, the food, or sometimes some food, depending on context

In У кота їжа в роті, English has to choose how to sound natural:

• The cat has food in its mouth
• A cat has food in its mouth

Usually context tells you which one is meant. In many learning examples, English uses the cat because it sounds more natural.

Yes, you could. It is grammatical.

• У кота є їжа в роті = The cat has food in its mouth

Adding є makes the existence/possession slightly more explicit. But in many everyday sentences, especially simple descriptive ones, Ukrainian often leaves є out:

• У кота їжа в роті

Both are understandable. The version without є is very common and natural.

Їжа is the general word for food.

In this sentence it means food in a broad sense. But depending on context, Ukrainian might use a more specific word, for example:

• м'ясо = meat
• риба = fish
• корм = pet food / feed

So:

• У кота їжа в роті = the cat has food in its mouth
• У кота риба в роті = the cat has fish in its mouth

Using їжа keeps it general.