Learn Italian: Il cane si è spaventato e io mi sono arrabbiato.

Because spaventarsi (to get scared) and arrabbiarsi (to get angry) are reflexive verbs. In the past tense, all reflexive verbs must use essere as their helper verb rather than avere.

The translation says 'got scared' and 'got angry'. Where is the word for 'got'?

Italian doesn't use a verb like 'to get' for changing emotions. Instead, it uses reflexive verbs. Spaventarsi literally means 'to scare oneself', and arrabbiarsi means 'to anger oneself'. So, si è spaventato is simply how Italians express 'it got scared'.

Why do the pronouns si and mi go before the helper verbs?

In the past tense, reflexive pronouns like mi (myself) and si (himself/itself) are always placed right before the helper verb. That is why we say si è spaventato and mi sono arrabbiato, keeping the pronoun and the helper verb together.

What if the person speaking is a woman? Does the sentence change?