system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we feel hot air when we expire air with our mouth open, but we feel fresh air when we blow air with our mouth "closed" as if we were whistling?
gpt
The air is actually hot, having been warmed by your body temperature. That's the warm "Haaaaaaaa" version.

A more closed mouth, though, pushes the air much faster, and it feels cool because fast blowing air wicks away heat & moisture (like an electric fan). It would not be cold to a thermometer no matter how fast you blow it out.