Why do we yawn and Why is yawning contagious?

WHAT IS YAWNING?

Yawning is such a familiar, automatic, and uncontrollable action that you may never have stopped to think about its components. You open your mouth wide, take a deep breath, and immediately exhale slowly. You may also close your eyes tight, causing them to water. In most cases, people feel more relaxed right after yawning.

So, that’s the experience. But what’s the reason for yawning?