Who Are You Calling an Idiom?

This one gets me all the time: Ever hear the expression "You can't beat a dead horse."? That, I believe, is a misconstrual of the phrase "You can't flog a dead horse." Now, "flog" has a couple meanings: it can indeed mean 'to whip or beat', so that the phrase means something like 'there's no sense in engaging in useless labor.' And that's its predominant use nowadays. But "flog" also means 'to sell or hawk', especially illegally. So the expression "You can't flog a dead horse" is actually an idiomatic expression of a British common law maxim. It's against the law to sell a horse that's already dead—unless, of course, it's for the purposes of glue or dog food or, lately, Ikea's Swedish meatballs. As with U.S. "lemon" laws w/r/t automobiles. Funny how language mutates.

Here's another: "He's the spitting image of his father." That's a bastardization of the phrase "spirit and image."

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Can you spot the influence?