Your cousins' granny really showed some idiomatic knowhow - she understood perfectly the semantics of 'being knocked up' in the Amur'can idiom. It was the supralinguistic elements (contextual appropriateness) that she wasn't clear on.

From my own background as an ESOL teacher overseas, imagine the looks of bewilderment when I praised a student's exceptionally astute (and well-phrased) comment in class by telling him, "You have a point."