Mettre son grain de sel

Literally: To add one's grain of salt

Example: “Personne ne lui a demandé son avis, mais il faut toujours qu'il mette son grain de sel.” — Nobody asked for his opinion, but he always has to put in his two cents.

English equivalent: To put in one's two cents

Origin: A 20th-century French rendering of the Latin tag cum grano salis, with a grain of salt — itself first written down by Pliny the Elder in his Natural History, in the form addito salis grano, describing a snake-venom antidote that called for one grain of salt added to the mix. Salt had long stood for wit and good sense in Latin (sal), so a grain of it dropped into someone else's business reads as a small, pointed contribution — offered whether or not it was wanted, which is exactly the mild reproach the French phrase carries.