Learn Russian: Актриса разговорилась с режиссёром. - The actress got into a conversation with the director.

It changes the meaning from simply "to speak" to "to get into a deep or flowing conversation." The prefix раз- combined with the postfix -ся (or -сь after a vowel) shows that an action has developed intensity or built up momentum. She didn't just speak; she really got talking.

How does разговорилась differ from заговорила? Don't they both mean she started talking?

They are different! The verb заговорить just marks the basic beginning of the action (she started speaking). In contrast, разговориться uses the developing intensity pattern. It means she warmed up to the conversation, opened up, and started talking freely or at length.

Why is the prefix spelled раз- here instead of рас-?

The prefix раз- changes to рас- only before voiceless consonants (like п, ф, к, т, ш, с). Because the root говор- begins with г, which is a voiced consonant, the з remains.

Is разговорилась perfective or imperfective?