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
songs of a highbrow type will find very few people to join in the chorus - qǔ gāo hè guǎ
the house is nearby but the person is far away - shì ěr rén yuǎn
Water carries the boat, water capsizes the boat - shuǐ zé zài zhōu,shuǐ zé fù zhōu