Here’s a fun read: Mark Peters in The Chronicle of Higher Education, writing about eggcorns.

So what’s an eggcorn? Originally, the word “eggcorn” was just an amusing misspelling of “acorn.” Linguists — especially those on the Language Log blog — noticed that “eggcorn” made a kind of intuitive sense and was an apt guess if you didn’t know the real spelling.

. . . All eggcorns makes sense on some level. For example, the eggcorn “girdle one’s loins” is far more understandable than the archaic “gird one’s loins.” “Free reign” — an extremely common misspelling — expresses a similar laxness to “free rein,” and there’s a kind of exclamatory kismet between “whoa is me!” and “woe is me!” Another eggcorn, “woeth me!” makes an old-fashioned-sounding word even more so. And since a rabble-rouser may eventually cause some rubble to exist, “rubble-rouser” is a nifty invention.

Lots more examples in the article, plus the delightful revelation that one Chris Waigl has an Eggcorn Database.

I know a fellow who used to coin them on purpose. Two of my favorites: “get to the crux of the biscuit” and “low dog on the scrotum pole” :-D