Introverts are very quiet… until they are around people they know and the conversation is on a subject which they know a lot about. Then you may see an introvert talk a lot. Sometimes this sudden conversationalist will surprise others. And the introvert may talk so much about a subject that it may almost seem that they are arrogant. But that person is not being arrogant. He/she is just very excited to feel comfortable enough to talk about a subject that is important to them.