Hard

That reminds me. My native-Dutch-speaking colleagues (who speak also quite fluent English, mind you) do manage from time to time to come up with some pretty funny idioms. The latest one I noticed was, "It's not hard rock science." I didn't correct him on that one (although I often do). Was that wrong? I didn't laugh out loud, either -- which I also often do. Probably the thing which then forces me to explain why and, subsequently, correct him.