People yawn because it is a common reflex that may serve multiple purposes, though the exact reasons are not fully understood. One popular theory is that yawning helps cool the brain by increasing blood flow and allowing cooler air to enter during a deep breath. This cooling effect could help improve alertness. Yawning also stretches the muscles in the skull and jaw, which may contribute to increased blood flow to the brain. Additionally, yawning is often linked to feelings of tiredness, boredom, or mild stress, and it might serve as a nonverbal way to communicate these states and connect socially with others. Yawning is contagious and is thought to be related to empathy, especially among people who are close to each other. In summary, yawning likely serves to cool the brain, regulate alertness, communicate state of mind, and foster social bonding. It can be spontaneous or triggered by seeing, hearing, or thinking about yawning in others.