В сильный мороз даже собака не хочет долго гулять и начинает дрожать у двери.

Мороз is in the accusative case here, and сильный agrees with it.

This is a common Russian pattern:

• в + accusative can be used in time or condition expressions
• в сильный мороз means something like in severe frost / when it is very cold

Why does сильный look the same as nominative? Because for a masculine inanimate noun, the accusative singular has the same form as the nominative:

• nominative: сильный мороз
• accusative: в сильный мороз

So the form does change by case grammatically, but in this specific type of noun, it happens to look identical.

Also, this phrase is idiomatic: Russian often says в мороз, в жару, в холод, etc. to describe weather conditions.

Yes, but the meaning is slightly different.

• в мороз = in frosty weather / when it is freezing
• на морозе = out in the cold / exposed to the frost

So:

• В сильный мороз даже собака не хочет долго гулять = When it’s very cold, even a dog doesn’t want to walk long
• На сильном морозе даже собака не хочет долго гулять would sound more like out in such severe cold...

Both are possible in the right context, but в сильный мороз is very natural for general weather conditions.

Даже means even.

In this sentence, it emphasizes собака:

• даже собака = even a dog

That means the speaker is stressing that dogs usually tolerate cold better than humans or like going outside, but in such weather even a dog doesn’t want to stay out long.

Its position matters. In Russian, даже usually stands close to the word it emphasizes.

Here:

• даже собака = it is the dog that is being emphasized

If you moved даже, the emphasis could change.

Собака is grammatically feminine, no matter whether the actual dog is male or female.

That is just how the noun works in Russian. So adjectives and past-tense verbs would normally agree with it as feminine:

• большая собака
• собака пришла

But in the present tense, Russian verbs do not show gender, so here you just get:

• собака не хочет
• собака начинает

If someone wants to specify a male dog, they can use пёс, which is a masculine noun. But собака is often used as the general word for dog.

Хотеть means to want, and in Russian it is commonly followed by an infinitive.

So:

• не хочет гулять = doesn’t want to walk / doesn’t want to go for a walk

Here:

• хочет = 3rd person singular present of хотеть
• гулять = infinitive

So literally the structure is:

• the dog does not want to walk

This is very normal Russian grammar:

• Я хочу спать = I want to sleep
• Он хочет есть = He wants to eat
• Собака не хочет гулять = The dog doesn’t want to go for a walk

Because гулять is the natural verb for taking a walk / going out for a walk / being out walking, especially for pets.

For a dog, гулять often means:

• to be walked
• to go out for a walk
• to spend time walking outside

So собака не хочет долго гулять is very natural.

Compare:

• идти = to go, to be going in one direction
• ходить = to go habitually / to walk around / to go back and forth
• гулять = to stroll, walk for pleasure, be out on a walk

For a dog owner, гулять с собакой is the standard expression for walking the dog.

Долго is an adverb, and it means for a long time.

So:

• долго гулять = to walk for a long time

This is not an adjective, so it does not change form. It simply modifies the verb.

Compare:

• долгий = long, as an adjective
• долго = long / for a long time, as an adverb

Examples:

• долгий день = a long day
• долго ждать = to wait a long time

So in the sentence, долго tells us how long the dog wants to walk: not very long.

This is a very common Russian structure:

• начинать + infinitive = to begin/start doing something

So:

• начинает дрожать = starts to shiver / begins to tremble

Breakdown:

• начинает = begins, starts
• дрожать = to tremble, shiver

Russian often uses this structure exactly the way English does:

• начинает говорить = starts speaking
• начинает плакать = starts crying
• начинает дрожать = starts shivering

Because дрожать describes an ongoing action or process: to tremble / to shiver.

After начинать, Russian often uses an imperfective infinitive when talking about starting an activity or process:

• начать читать = to start reading
• начать работать = to start working
• начать дрожать = to start shivering

Shivering is not a single completed act; it is a continuing physical reaction. So the imperfective verb fits naturally.

You could also meet a verb like задрожать, which means to begin trembling in a more compact way. But начинает дрожать is very clear, neutral, and natural.

After у, Russian uses the genitive case.

So:

• dictionary form: дверь
• after у: у двери

Here у двери means:

• by the door
• near the door
• at the door

This suggests the dog is standing near the door, probably wanting to go back inside.

Some useful parallels:

• у дома = by the house
• у окна = by the window
• у двери = by the door

So the key grammar point is simple: у + genitive.

Because Russian does not need to repeat the subject when the same subject clearly applies to both verbs.

So:

• собака не хочет долго гулять и начинает дрожать у двери

means:

• the dog doesn’t want to walk long and starts shivering by the door

The subject собака belongs to both:

• не хочет
• начинает

English works the same way here:

• The dog doesn’t want to walk long and starts shivering
• not necessarily The dog doesn’t want to walk long and the dog starts shivering

Repeating the noun in Russian would usually be unnecessary.

The given word order is quite natural and neutral:

• В сильный мороз даже собака не хочет долго гулять и начинает дрожать у двери.

Russian word order is flexible, but changes often affect emphasis rather than basic meaning.

For example:

• Даже собака в сильный мороз не хочет долго гулять...
  • puts early emphasis on even a dog
• У двери собака начинает дрожать
  • highlights the location more strongly

The original sentence flows naturally from:

1. the situation: в сильный мороз
2. the surprising subject: даже собака
3. the actions: не хочет гулять and начинает дрожать

So yes, it can be changed, but the version you have is a very normal, standard way to say it.

It can be understood as a general present: what typically happens in such weather.

Russian present tense often covers both:

• what is happening now
• what generally happens

So this sentence can mean:

• In severe frost, even a dog doesn’t want to walk long and starts shivering by the door

That sounds like a general statement about behavior in very cold weather.

If the speaker wanted to describe one completed past event, Russian would likely use past tense forms instead:

• не хотела
• начала дрожать

But in the current sentence, the present tense sounds like a general observation or vivid description.

Because Russian has no articles like a, an, or the.

So:

• собака can mean a dog or the dog
• двери can mean a door or the door, depending on context

Russian relies on:

• context
• word order
• shared knowledge
• sometimes intonation

In this sentence, English would naturally use:

• even a dog
• by the door

But Russian simply says собака and двери without articles. That is completely normal.