欸 (ēi) is an interjection used to call someone's attention, similar to 'hey!' in English. It is always placed at the beginning of an utterance, often followed by a comma or exclamation mark. The tone can vary: ēi (first tone) for neutral calling, éi (second tone) for surprise or question, èi (fourth tone) for disappointment or acknowledgment. The most common for drawing attention is ēi.