《论衡·卷二十三·言毒篇》
由于生在低处，潮湿靠近阴气的地方，这些阴物都是软体曲伸爬行的，所以蝮蛇用口咬人。
生下湿比阴，阴物柔伸，故蝮蛇以口齰。
Because they are born in low, humid places close to yin qi, these yin things are soft, bend and crawl, so vipers bite people with their mouths.