ἐν πέτροισι πέτρον ἐκτρίβων → by grinding stone against stones
embŏlĭum: ii, n., = ἐμβόλιον,I something thrown in; in scenic lang., an interlude, ballet, Cic. Sest. 54, 116 (embolia pertinent ad gestus saltatorios, Schol.).