an extra thumb
Pinyin is pi á nm ǔī zh ǐ, which means to compare superfluous and useless things. It comes from Zhuangzi's parallel thumb.
Idiom explanation
Parallel mother: the thumb on the foot and the second toe form one toe; branch finger: the thumb on the hand gives birth to one more finger.
The origin of Idioms
In Zhuangzi's parallel thumb: "parallel thumb is beyond nature, but extravagant in virtue."
Idiom usage
It's a combination; it's a subject, a predicate, an object; it's a metaphor for superfluous and useless things. example this is not a demon. It's different from others. Can you call it a demon? (notes of Yuewei thatched cottage, Volume 11, by Ji Yun of Qing Dynasty)
an extra thumb
use lame arguments and perverted logic - qiǎng cí duó lǐ
excellent in both performing skills and moral integrity - dé yì shuāng xīn
the road to happiness is strewn with setbacks - hǎo shì duō mó
follow in the steps of one 's ancestors - shéng qí zǔ wǔ
price oneself out of the market - màn tiān yào jià