Szelki są wygodniejsze od obroży, ale kaganiec biorę ze sobą zawsze, kiedy jedziemy metrem.

Szelki is normally treated as a plural noun when it means a harness or suspenders/braces. Because of that, it takes a plural verb, so you get szelki są = the harness is / harnesses are.

This is one of those nouns that refers to a single item in English but is often plural in Polish, because it is thought of as something made of connected straps.

So:

• szelki są wygodne = the harness is comfortable
• not usually szelka jest... for this meaning

Because this is a comparative adjective: wygodniejsze means more comfortable.

The basic adjective is:

• wygodny = comfortable

Its comparative is:

• wygodniejszy / wygodniejsza / wygodniejsze

Here it agrees with szelki, which is plural non-masculine-personal, so the correct form is:

• szelki są wygodniejsze

Compare:

• pies jest wygodniejszy — uncommon logically, but grammatically masculine singular
• obroża jest wygodniejsza — feminine singular
• szelki są wygodniejsze — plural non-masculine-personal

In Polish, one very common way to make comparisons is:

• X jest ... od Y = X is ... than Y

So:

• wygodniejsze od obroży = more comfortable than a collar

After od, Polish uses the genitive case, so obroża changes to obroży.

This pattern is extremely common:

• lepszy od tego = better than that
• większy od domu = bigger than the house
• tańszy od samochodu = cheaper than the car

The dictionary form is:

• obroża = collar

In the sentence, after od, it becomes genitive singular:

• od obroży

So the change is:

• obroża → obroży

That is a normal change for many feminine nouns ending in -a.

It is the accusative singular, because it is the direct object of biorę:

• biorę kaganiec = I take a muzzle

However, for many masculine inanimate nouns, the accusative looks exactly like the nominative. So:

• nominative: kaganiec
• accusative: kaganiec

That is why the form does not visibly change.

Brać ze sobą is a very common expression meaning to take with oneself, or more naturally in English, to take along / to take with me.

So:

• kaganiec biorę ze sobą = I take the muzzle with me / I take the muzzle along

The part sobą comes from siebie and means oneself in this kind of structure.

You will often see:

• biorę ze sobą telefon = I’m taking my phone with me
• weź ze sobą wodę = take water with you
• zabrałem ze sobą dokumenty = I took the documents with me

Polish sometimes uses ze instead of z for easier pronunciation.

Before sobą, the usual form is:

• ze sobą

This is just a phonetic variant of z. You also see this in other phrases, for example:

• ze szkoły
• ze mną
• ze względu na

So here, ze sobą is simply the normal, natural form.

Because Polish usually omits subject pronouns when they are clear from the verb ending.

For example:

• biorę already means I take
• jedziemy already means we go / we ride

So adding ja or my is often unnecessary unless you want emphasis or contrast.

Compare:

• Biorę kaganiec. = I take the muzzle.
• Ja biorę kaganiec. = I take the muzzle. (emphatic)

Jedziemy means we go / we are going / we ride, while jadę means I go / I am going.

The speaker uses we, probably meaning something like:

• the speaker and the dog
• the speaker and another person
• the speaker and whoever is traveling together

Since Polish often leaves out subject pronouns, jedziemy by itself already tells you the subject is we.

Because after jechać when you say by means of transport, Polish normally uses the instrumental case.

So:

• metro = nominative
• metrem = instrumental

This is the same pattern as:

• jadę autobusem = I’m going by bus
• jedziemy pociągiem = we’re going by train
• pojechał samochodem = he went by car
• jedziemy metrem = we’re going by metro

Yes. Here kiedy introduces a time clause:

• kiedy jedziemy metrem = when we go by metro

With zawsze, the whole phrase means something like:

• always when
• more natural English: whenever

So the sentence could be understood as:

• I always take a muzzle with me whenever we go by metro.

Because kiedy jedziemy metrem is a subordinate clause, and in Polish subordinate clauses are normally separated by a comma.

So:

• ..., kiedy jedziemy metrem

This is standard Polish punctuation.

The same happens with other conjunctions:

• Wiem, że przyjdzie. = I know that he’ll come.
• Zadzwonię, kiedy wrócę. = I’ll call when I return.
• Zostań, jeśli możesz. = Stay if you can.

Yes. In this sentence, kiedy and gdy would both work.

For example:

• ...zawsze, kiedy jedziemy metrem
• ...zawsze, gdy jedziemy metrem

Both mean basically the same thing here. Gdy can sound a little more written or formal in some contexts, but both are very common.

You might also hear jak in some kinds of speech, but kiedy and gdy are the safest standard choices.

Yes, at least a little. Polish word order is flexible, and different orders can shift emphasis.

Starting with kaganiec gives it some contrastive focus, especially after the first clause about szelki and obroża. It feels a bit like:

• Harnesses are more comfortable than collars, but a muzzle I always take with me...

A more neutral order could also be:

• Ale zawsze biorę ze sobą kaganiec, kiedy jedziemy metrem.

Both are grammatical. The original version puts a bit more attention on kaganiec.