Why do people who watch incense yawn?

1, tired, but this is not too much.

2, lack of mindfulness, just because I have studied in the past, such as Confucianism, Taoism, and then Buddhism.

At that time, their teaching was completely different from their spiritual practice, so there was a mutually exclusive process, and he would yawn. Especially those who believe in immortals, if you tell him Buddhism, he will yawn. Including those of us who believe in Buddhism at first, or those who don't believe in Buddhism, if we recite Buddhist scriptures, even if we read the Heart Sutra, his tears will drip down and yawn one after another, and then he will fall asleep.