Expressions in your world

On January 14, 2014, J. Garf wrote, What's a good way to come up with figures of speech? There are things we all say every day, and I feel like a few of these add color to a story, but some expressions just don't make sense. For example, you can't exactly say "what on earth is that?" if your story doesn't take place on earth. Another good one that doesn't work is "holy cow!" I use this one all the time in daily speech but can't in my book because it originated because of Hindus’ beliefs that...