An opposite Example

反面例子
An aesthetics professor's grandson asked his grandfather. "Grandpa, why did you say that all the father are ugly?"
一位美学教授的孙子问他：“爷爷，为什么你总说所有假的东西都是丑陋的呢？”
"That's certainly true. Couldn't you give me an opposite example?"
“那是当然了。难道你能给我举个反面例子吗？”
"Oh, yes," the grandson, climbing on his grandfather's knees, said proudly, "Look at yourself. When you put on your false teeth, you looked younger and lively; when you get off them, your mouth looked empty and shriveled, that's really ugly. Isn't it an opposite example?"
“哦，当然啦。”孙子爬上爷爷的膝盖，自豪地说，“看看你自己。你带上假牙，看起来既年轻又有活力；拿下假牙，你的嘴看起来就空空的，还皱巴巴的，真的很难看。这不是个反面例子吗？”
The professor could find no answer.
教授无言以对。