One of the entertaining features that editor Tom Sumner created for my Common Errors in English Usage book is the list of ”mangled expressions“ beginning on p. 276. It contains a few instances where two common sayings have been cross-pollinated, creating odd hybrids.
Examples include “cast in stone,” “face the piper,” and “mumble jumbo.”
More are listed on my “More Errors” page, including “by the same hand,” “pick fun,” “pin a finger,” “tooth and tong,” and “worth its weight in salt.”
I just heard another example on the radio when a journalist covering sports spoke of a “school of thumb” which sounds like a hybrid of “school of thought” and “rule of thumb.”
An electronica band in Minneapolis named itself “School of Thumb.”
The band seems to have had a short and rather obscure existence, so it hasn’t spread the mangled expression much; but it’s probably a natural mutant which pops up from time to time.