一颗老鼠屎坏了一锅汤

yī kē lǎo shǔ shǐ huài le yī guō tāng

lit. one pellet of rat feces spoiled the whole pot of soup (idiom)

fig. one bad apple can spoil the whole bunch

一

yī

one

颗

kē

classifier for small spheres, pearls, corn grains, teeth, hearts, satellites etc

老

lǎo

prefix used before the surname of a person or a numeral indicating the order of birth of the children in a family or to indicate affection or familiarity

鼠

shǔ

(bound form) rat; mouse

屎

shǐ

feces; excrement; a stool

坏

huài

bad

了

le

(completed action marker)

一

yī

one

锅

guō

pot; pan; wok; cauldron

汤

tāng

soup