also: ナメクジにしお
expression
crestfallen; dejected; like a slug sprinkled with salt
Idiomatic expression describing someone who looks utterly deflated, wilted, or discouraged, as if they have shriveled up like a slug when salt is put on it.
彼は上司に叱られて、蛞蝓に塩のようだった。
After being scolded by his boss, he looked as crestfallen as a slug sprinkled with salt.
From the image of a slug shriveling up when salt is sprinkled on it, used metaphorically for a person who appears deflated or dejected.