對牛彈琴 wasted effort

對 (before) 牛 (cow) 彈 (play) 琴 (piano)

琴 can refer to other musical instruments, mostly string instruments

三角琴 grand piano

What do you suppose you are doing? Perhaps you are casting pearls before swine?

Shouldn't you save your zippy zithery music for a being who might relate to you?

Similarly, 牛耳讀經

牛 (cow) 耳 (ear) 讀 (read) 經 (classics)

Classics before cows? Or string theory. Your choice to waste.

飛蛾赴火 a moth to a flame

飛 (fly) 蛾 (moth) 赴 (approach) 火 (fire)

simplified,
飞蛾赴火

Thus hath the candle singd the moath...

A moth with a death wish.

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“The construction trash was flying through the air in a surreal picture reminiscent of some eerie scene out of Poltergeist, drawn toward the fire by the vacuum, like the proverbial moth to the candle flame." - Santa Barbara Independent