Mettre l'eau à la bouche

Literally: To put water in the mouth

Example: “L'odeur des croissants chauds me met l'eau à la bouche.” — The smell of warm croissants makes my mouth water.

English equivalent: To make one's mouth water

Origin: Purely physiological to start with: anticipating good food triggers real salivation, and French had l'eau en vient à la bouche for exactly that from the 15th century, with Rabelais using the same image for appetite in the 16th. What changed over time was the direction of the metaphor. Originally the phrase reported a fact about your own body — the water was already arriving, an observation about yourself — and only in the 17th century did it flip into something one thing or person does to another: a smell, a sight, or a tempting offer now causes the reaction in someone else, rather than simply describing your own.