What 'nostril's hair move' have to do with fear? (嚇到鼻哥窿都冇肉) 嚇到鼻哥窿都冇肉 literally means 'Scared to the point of even nostrils have no flesh'
I was wondering what 'nostrils have no flesh' have to do with fear, so I did some search and found the following article:

【粵語講呢啲】


舊時廣東人在感受到極度驚嚇時多會說這句話。究竟這與「鼻孔有沒有肉」何干呢？人在此時，反應就是廣東人所講的「嚇到震晒」（身體顫抖不已）；誇張點說，就連鼻這部位都會抖震。鼻震動，鼻孔內的毛隨之而震動，所以「嚇到鼻哥窿『都冇肉』」原來指「嚇到鼻哥窿『啲毛喐』」，難怪人們聽後不明所以了。

It said 都冇肉 /dou1 mou5 juk6/ (have no flesh) was a mispronunciation of 啲毛喐 /di1 mou4 juk1/ (the hair move)
Now, I am wondering, What is the logic behind this idea.
Wayne Cheah wrote:

You are so struck with fear that your whole body trembles right to the nostril hairs, with the heavy breathing and all? Perhaps with less emphasis on personal male grooming in the old days, nostril hairs were allowed to grow much longer than now, and you could even see someone's nostril hairs tremble in fear?

Good thinking. If you have a full beard that covers your entire lower face,  most of the beard would shake when you are tumbling due to fear, but the bread under your nostril is closer to the root and tighter to your skin, therefore won't tumble and move like the rest of the bread. However, when you are extremely scared, your breathing will become heavy and the air you exhale would move that part of the bread that normally wouldn't move.
Similar logic behind 怒得吹鬚睩眼 (So angry that your bread is being blown to move and your eyes grow big)