down in the mouth

Example: “Why so down in the mouth? Did the interview go badly?”

Origin: Describes a real and involuntary facial signal. Sadness pulls the corners of the mouth downward through a muscle that acts largely outside conscious control, and Darwin singled out this movement in The Expression of the Emotions in Man and Animals (1872) as one of the expressions that appears across cultures without being learned. That universality is why the phrase reads instantly rather than requiring explanation: the downturned mouth is legible to anyone. It is attested in English from the 1600s, appearing in print by the 1640s, and belongs to a large family of idioms that locate a mood in the visible position of a body part — chin up, head held high, shoulders slumped, face falling.