Laughter improves respiration and activates our immune system.笑能改善呼吸并激活我们的免疫系统。This activates the body's thirst mechanism.这会触发身体的口渴机制。Sunlight activates a chemical reaction in the plant's leaves.在阳光的照射下,植物叶子中会发生一种化学反应。This activates the train's tilt mechanism.这就能启动火车的倾斜装置。