Imagine you are watching a horror movie. The music builds. The protagonist walks slowly toward the dark door. Your muscles tense up. You hold your breath. The door creaks open... and it's just a cat!
You let out a loud, almost aggressive laugh.
That isn't necessarily because the cat is "funny." It's because you had built up a massive amount of physiological tension, and now that the threat is gone, that energy needs to go somewhere. This is the Relief Theory of humor.
The Hydraulic Model
Proposed by Herbert Spencer and later adopted by Freud, Relief Theory views the nervous system like a steam engine. We build up steam (nervous energy) in response to emotions like fear, anger, or sexual tension.
If that energy isn't used for action (fighting the monster or running away), it becomes "excess." Laughter is the safety valve that releases this excess energy to restore equilibrium.
Why We Laugh at Taboos
This theory explains why jokes about taboo subjects—sex, death, politics—are so popular. Society forces us to repress our natural impulses regarding these topics. This repression takes mental energy.
When a comedian tells a dirty joke, they briefly lift that repression. The energy we were using to hold back our thoughts is suddenly released. The "explosion" of laughter is the sound of that psychological pressure dropping.
Nervous Laughter
This is also why we sometimes laugh at inappropriate times, like during a funeral or a serious reprimand. It's not that we find the situation amusing; it's that the situation is creating an unbearable amount of tension, and our body triggers laughter as a panic button to release it.
Conclusion
Laughter isn't always about joy. Sometimes, it's just a sign that we survived the tension. It's the body's way of saying, "Phew, that was close."