system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does your voice sound different when tired?
gpt
Your voicebox is essentially two flappyflaps that can vibrate at different frequencies, tight flaps is high pitch, loose flaps is low pitch. These flaps are controlled by muscles. When you are tired or really relaxed, your flappyflaps are a bit looser than usual because of the relaxed muscles, and your voice will be a bit deeper as a result.