La vétérinaire dit que le harnais est plus pratique que la laisse pour ce chiot.

Vétérinaire can be used for either a male or a female vet. The noun itself usually stays the same, and the article shows the gender:

• le vétérinaire = the male vet
• la vétérinaire = the female vet

So in this sentence, la vétérinaire tells you the speaker is referring to a woman.

Because the subject is la vétérinaire, which is she.

The verb dire in the present tense goes like this:

• je dis = I say
• tu dis = you say
• il/elle dit = he/she says

So la vétérinaire dit means the vet says.

They are spelled the same, but they do different jobs here.

• dit que = says that
• plus pratique que = more practical than

So:

• the first que introduces what the vet says
• the second que is part of the comparison

This is very common in French. The same word can have different meanings depending on the structure around it.

This is the normal French pattern for more ... than:

• plus
  • adjective + que

So:

• plus pratique que = more practical than
• plus grand que = bigger than
• plus cher que = more expensive than

In this sentence, le harnais est plus pratique que la laisse means the harness is being compared with the leash.

French often uses the definite article where English might use either the or a/an, especially when talking about things as general options or known items in the situation.

Here, le harnais and la laisse present the two choices being compared:

• the harness
• the leash

If you said un harnais and une laisse, that would still be possible in some contexts, but it would sound more like a harness and a leash in a more indefinite, less specific way.

Adjectives do agree with the noun they describe, and here pratique describes le harnais.

But the adjective pratique has the same form in both masculine singular and feminine singular:

• un objet pratique
• une solution pratique

So agreement is still happening, but you do not see a different ending here.

You would only clearly see a change in the plural:

• des objets pratiques

Because pour here means for in the sense of for the benefit of or suitable for.

So plus pratique ... pour ce chiot means more practical for this puppy.

Using à would not express that idea naturally here. À often means to, at, or marks an indirect object, but that is not what is needed in this sentence.

Because chiot is a masculine singular noun that begins with a consonant sound.

French uses:

• ce before a masculine singular noun starting with a consonant sound
• cet before a masculine singular noun starting with a vowel or mute h
• cette before a feminine singular noun

So:

• ce chiot = correct
• cet animal = correct
• cette laisse = correct

Because le harnais is already the clear subject of the sentence.

French normally uses a plain form of être after a specific subject:

• Le harnais est pratique.
• La laisse est légère.

C'est is more common when introducing or identifying something in a less direct way:

• C'est pratique.
• C'est un harnais.

So here, since the subject is explicitly le harnais, est is the natural choice.

Yes, but the original position is the most natural.

The sentence ends with pour ce chiot because that phrase applies to the whole comparison:

• La vétérinaire dit que le harnais est plus pratique que la laisse pour ce chiot.

You could also say:

• Pour ce chiot, la vétérinaire dit que le harnais est plus pratique que la laisse.

That version puts extra emphasis on for this puppy. Both are correct, but the original sounds more neutral and natural in everyday French.