Нельзя выпускать щенка без ошейника, даже если двор кажется тихим.

Here нельзя means something like it is not allowed, you must not, or one shouldn’t.

In this sentence, it is not mainly about physical inability. It is about a rule, prohibition, or strong recommendation:

• Нельзя курить. = Smoking is not allowed.
• Нельзя выпускать щенка без ошейника. = You must not let the puppy out without a collar.

Russian often uses нельзя + infinitive for general prohibitions.

Because Russian often leaves out the subject when it is general or obvious.

Нельзя выпускать щенка... is an impersonal construction. It does not literally say you must not, but that is the natural English translation.

It has the sense of:

• It is not allowed to let the puppy out...
• One must not let the puppy out...
• You shouldn’t let the puppy out...

This is very common in Russian, especially with words like можно, нельзя, надо, нужно.

This is about verbal aspect.

• выпускать = imperfective
• выпустить = perfective

Here the imperfective выпускать is used because the sentence expresses a general rule or habitual situation, not one single completed action.

So:

• Нельзя выпускать щенка без ошейника.
  = You must not let the puppy out without a collar in general.

If you said:

• Нельзя выпустить щенка без ошейника.

that would sound more like a specific single act: You must not let the puppy out this one time without a collar.

In general instructions and rules, Russian very often prefers the imperfective.

Because щенка is the direct object, and щенок is an animate masculine noun.

For animate masculine nouns in the singular, the accusative form looks like the genitive form.

So:

• nominative: щенок = puppy
• accusative: щенка = puppy as the object

Compare:

• Щенок спит. = The puppy is sleeping.
  Here щенок is the subject.
• Я вижу щенка. = I see the puppy.
  Here щенка is the object.

The same thing is happening in your sentence: the puppy is what is being let out, so Russian uses щенка.

Ошейника is in the genitive singular because the preposition без always takes the genitive.

• без ошейника = without a collar

Some more examples:

• без воды = without water
• без поводка = without a leash
• без куртки = without a jacket

So this part is a very useful fixed pattern:

• без + genitive

Because after казаться (to seem), Russian often uses the short descriptive part in the instrumental case.

So:

• двор кажется тихим = the yard seems quiet

Here:

• тихий = nominative masculine singular
• тихим = instrumental masculine/neuter singular

This instrumental after казаться is very common and standard.

More examples:

• Он кажется уставшим. = He seems tired.
• Дом кажется пустым. = The house seems empty.

So тихим is not random; it is the normal form after кажется.

Because двор is the subject of кажется.

The structure is:

• двор кажется тихим
  literally: the yard seems quiet

So двор is in the nominative case.

If you said во дворе, that would mean in the yard, which is a different role in the sentence.

Compare:

• Двор кажется тихим. = The yard seems quiet.
• Во дворе тихо. = It is quiet in the yard.

Both are possible Russian ideas, but they mean slightly different things.

In this context, выпускать means to let out, to let go outside, or to allow to go out.

With a pet, it often means letting the animal go outside into a yard, street, or open area.

So here it is not about publishing or releasing in a formal sense, even though выпускать can have other meanings in other contexts, such as:

• выпускать книгу = to publish a book
• выпускать продукцию = to produce/manufacture goods

In your sentence, the pet context makes the meaning clear: let the puppy out.

Даже если means even if.

It introduces a clause that says the main statement is still true despite some possible condition.

So:

• Нельзя выпускать щенка без ошейника, даже если двор кажется тихим.
• You must not let the puppy out without a collar, even if the yard seems quiet.

This means: the yard seeming quiet does not change the rule.

Compare:

• Если двор тихий, можно выйти. = If the yard is quiet, you can go out.
• Даже если двор тихий, нельзя выпускать щенка без ошейника. = Even if the yard is quiet, you must not let the puppy out without a collar.

So даже если adds the idea of despite that.

Because даже если двор кажется тихим is a subordinate clause.

Russian normally separates subordinate clauses from the main clause with a comma.

Main clause:

• Нельзя выпускать щенка без ошейника

Subordinate clause:

• даже если двор кажется тихим

So the comma is standard Russian punctuation here.

Двор usually means yard, courtyard, or the outdoor area around a house or building.

It is not exactly the same as:

• сад = garden
• улица = street

So in this sentence, двор suggests an enclosed or semi-enclosed outside area near the home. That is why the yard seems quiet is a natural translation.

Depending on context, двор can also mean the shared courtyard area in front of apartment buildings.

Yes. Russian word order is flexible.

This sentence could be rearranged, for example:

• Даже если двор кажется тихим, нельзя выпускать щенка без ошейника.

This means the same thing, but it puts more emphasis on the even if clause first.

The original version starts with the rule itself:

• Нельзя выпускать щенка без ошейника...

That sounds very natural, because the prohibition is the main point.

It usually sounds like a fairly strong rule or prohibition.

Because of нельзя, it is stronger than something like:

• не стоит = it’s not a good idea
• лучше не = it’s better not to

So:

• Нельзя выпускать щенка без ошейника
  sounds closer to
• You must not let the puppy out without a collar

In real life, the exact strength depends on context. A parent, pet owner, or safety guide might use it as a firm instruction.

In this sentence, ошейник clearly means an animal’s collar, especially a dog collar.

The word is normally used for the collar worn by an animal around its neck.

So:

• щенок без ошейника = a puppy without a collar

In context, it suggests a safety or control issue: the puppy should not be outside without wearing one.