There are some phrases that have, or at least originally had, a meaning that was cleverly expressed in a metaphor or an allusion, but which now are too often used in a banal and thoughtless way. I have collected some instances. Maybe others will think of other examples.
"The proof is in the pudding. " This is a degraded version of the saying "The proof of the pudding is in the eating. " The original saying is coherent, witty, and pointed; the mangled version is witless and senseless. The original phrase means that if something is made for a certain purpose, then the proof (i.e., the test) of its merit is how well it fulfills that purpose. As a pudding is made to be eaten, so the proof of it is in the eating. The idea is not that if you want proof of something, you should look in a pudding, as the idiotic mangled version of the saying has it.
"Sour grapes." Contrary to popular understanding, this does not mean being bitter about losing. It means disparaging something that you wanted but failed to obtain. It comes from a fable of Aesop, in which a fox that is unable to reach a bunch of grapes goes away saying that the grapes were probably sour anyway. (I thought that the fable was ridiculous until I read somewhere, to my surprise, that foxes actually do like grapes!)
"To play cat and mouse." Sometimes, when a cat catches a mouse, it does not kill it, but lets it go free for a moment, only to catch it again repeatedly, as if playing a cruel game with its victim. (I have heard that mother cats do this before their kittens to train them to catch mice.) To play with someone who is in your power in an analogous fashion is to "play cat and mouse" with that person. The phrase does not mean hunting after someone.
"The proof is in the pudding. " This is a degraded version of the saying "The proof of the pudding is in the eating. " The original saying is coherent, witty, and pointed; the mangled version is witless and senseless. The original phrase means that if something is made for a certain purpose, then the proof (i.e., the test) of its merit is how well it fulfills that purpose. As a pudding is made to be eaten, so the proof of it is in the eating. The idea is not that if you want proof of something, you should look in a pudding, as the idiotic mangled version of the saying has it.
"Sour grapes." Contrary to popular understanding, this does not mean being bitter about losing. It means disparaging something that you wanted but failed to obtain. It comes from a fable of Aesop, in which a fox that is unable to reach a bunch of grapes goes away saying that the grapes were probably sour anyway. (I thought that the fable was ridiculous until I read somewhere, to my surprise, that foxes actually do like grapes!)
"To play cat and mouse." Sometimes, when a cat catches a mouse, it does not kill it, but lets it go free for a moment, only to catch it again repeatedly, as if playing a cruel game with its victim. (I have heard that mother cats do this before their kittens to train them to catch mice.) To play with someone who is in your power in an analogous fashion is to "play cat and mouse" with that person. The phrase does not mean hunting after someone.