prendre des vessies pour des lanternes

You use this phrase to call out a lie. You can use it when someone tries to trick you. It usually follows the verb prendre. For example: Il me prend pour une imbécile. Or more specifically: Il essaie de me faire prendre des vessies pour des lanternes. It functions as a colorful way to say 'You can't fool me.'

Use it when a politician makes a promise that sounds too good. Use it when a salesperson exaggerates a product's benefits. It is perfect for debates or heated discussions. You might use it while watching a movie with a plot hole. It works well when gossiping about a friend's questionable new crush. It adds a bit of bite to your criticism.

Do not use this in a very formal legal document. It is a bit too colorful for a funeral or a somber event. Avoid using it if you want to be extremely polite. It implies the other person is either a liar or a fool. Use it carefully with your boss. You do not want to suggest they are delusional! Unless, of course, they are.

This expression dates back to the 13th century. Back then, dried bladders were actually used as makeshift lanterns. They were translucent and could hold a candle. However, they were cheap and smelled bad. Real lanterns were made of glass or parchment. Mistaking one for the other was a sign of being easily tricked. It has survived centuries because the imagery is so vivid.

You will mostly hear the standard version. Sometimes people just say Il essaie de nous vendre des vessies. This implies the 'lantern' part without saying it. In modern slang, you might hear Il nous mène en bateau. But vessies remains the classic, more sophisticated way to describe a scam. It sounds a bit old-fashioned, which gives it more charm.