Tener mala leche

Meaning: To be in a foul mood or have bad intentions.

Language: Spanish

Literally: To have bad milk

Category: Food & Drink

Origin: Rests on an ancient belief, already discussed by Aristotle and later Saint Augustine, that a nursing infant's character was shaped by the milk it drank — not just nutritionally, but temperamentally. In medieval Spain, families wealthy enough to hire a wet nurse rather than have the mother breastfeed vetted their choice carefully, since the nurse's own health, background, and even moral character were thought to pass directly into the child through her milk. "Mala leche" — bad milk — meant a nurse (or a mother) whose milk had transmitted a genuinely bad temperament, and the phrase kept that sense of an ingrained, almost inherited character flaw long after the underlying medical belief was abandoned.