Ο κτηνίατρος έχει εμβολιάσει, στειρώσει και αποπαρασιτώσει το κατοικίδιο· το κοινωνικοποιώ.

It is the Greek equivalent of the present perfect: has vaccinated, spayed/neutered, and dewormed / treated for parasites.

It is built with:

• έχει = has
• a special verb form such as εμβολιάσει, στειρώσει, αποπαρασιτώσει

A useful point for English speakers: Modern Greek does not use an infinitive the way English does. So after έχει, Greek uses this dependent perfective form instead of something like to vaccinate.

Because all three actions share the same subject and the same tense.

So Greek can say:

• έχει εμβολιάσει, στειρώσει και αποπαρασιτώσει

instead of repeating:

• έχει εμβολιάσει, έχει στειρώσει και έχει αποπαρασιτώσει

Both ideas are understandable, but using just one έχει is the normal, natural way when the verbs are coordinated.

That ending is very common in the perfective dependent form of many verbs in -ώνω / -ώ / -άζω / -ίζω and similar patterns.

Here are the dictionary forms:

• εμβολιάζω → εμβολιάσει
• στειρώνω → στειρώσει
• αποπαρασιτώνω → αποπαρασιτώσει
• κοινωνικοποιώ → κοινωνικοποιήσει in the same kind of perfective dependent form

Important: εμβολιάσει by itself is not a normal standalone past tense in this sentence. It works together with έχει.

It means it and refers back to το κατοικίδιο.

So:

• το κατοικίδιο = the pet
• το κοινωνικοποιώ = I socialize it / I am socializing it

Greek very often uses a short object pronoun like το instead of repeating the full noun again.

Because weak object pronouns in Modern Greek normally come before the verb.

So Greek says:

• το κοινωνικοποιώ = I socialize it

not:

• κοινωνικοποιώ το as the normal neutral word order

This is one of the most important differences from English. In English, object pronouns usually come after the verb; in Greek, these short clitic pronouns usually come before it.

Greek is a pro-drop language, which means subject pronouns are often omitted because the verb ending already shows the person.

• κοινωνικοποιώ = I socialize / I am socializing

The ending tells you it is first person singular.

So the sentence does not need εγώ. If you added εγώ, it would sound more emphatic, like I’m the one socializing it.

Yes. κατοικίδιο is a neuter singular noun.

That is why you get:

• το κατοικίδιο = the pet
• το κοινωνικοποιώ = I socialize it

The pronoun agrees with the noun’s gender and number, so a neuter singular noun takes το.

That mark is called the άνω τελεία in Greek.

In modern usage, it usually marks a pause stronger than a comma. In English, it often corresponds roughly to:

• a semicolon
• or sometimes a colon-like pause

Here it separates two closely related parts:

• what the vet has already done
• what I am doing now

So it is functioning a lot like a semicolon in English.

Because the two parts describe different kinds of actions:

• Ο κτηνίατρος έχει εμβολιάσει, στειρώσει και αποπαρασιτώσει...
  These are presented as completed actions with relevance now.

• το κοινωνικοποιώ
  This is a present action, so it means I socialize it or I am socializing it.

This contrast is very natural: the vet has already done the medical procedures, while the speaker is currently doing the socialization.

It can mean either, depending on context.

The Greek present tense often covers both:

• a general / habitual meaning: I socialize it
• an ongoing meaning: I am socializing it

If the wider context is about the current process of caring for the pet, I am socializing it is often the most natural reading.

It can mean either.

Greek στειρώνω is a general verb for sterilizing an animal, so in English the best translation depends on the animal’s sex:

• female animal → spay
• male animal → neuter

So στειρώσει does not force the same distinction that English often makes.

Greek uses the definite article very regularly, often more often than English does.

Here:

• ο κτηνίατρος = the vet
• το κατοικίδιο = the pet

This suggests we are talking about a specific, identifiable vet and a specific pet, not just any vet or any pet.

For English speakers, one useful habit is: if a Greek noun is specific, expect an article very often.