Here's a little something I learned while writing A MADNESS SO DISCREET. I was working on a scene where a character needed to say something along the lines of, "Somebody call the cops!" Now, aside from the fact that they wren't calling anyone, I couldn't finish the sentence because I didn't know what policemen were called in Boston in the 1890s.
Were they police? Constables? Bobbies?
Ironically, I don't actually remember what the answer was, but I learned something cool while trying to find out.
The reason why we call police "cops" is because their badges were originally made out of copper - hence they were first called "coppers" which became shortened to "cops."
Fifteen minutes worth of research later, I was able to finish my one line of dialogue.
And I got a blog post out of it :)