Do you want to know from where "writing on the wall" expression came?

>I used the "writing on the wall" expression in this thread or another and wondered if the recipient - Cetin - would understand that one. Also, I couldn't help but wonder where it came from. My sister had a book about expression such as these and where they came from, but these days she says she doesn't know what book I'm talking about. But there has to be one out there somewhere . . .
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>>FWIW, knee jerk essentially means "reflex" or "without thought." Comes from when you go to the doctor and he checks your reflexes hitting you on the knee with the instrument to check your reflexes.