HARROW : An agricultural implement used as an instrument of torture (2 Samuel 12:31; 1 Chronicles 20:3)
MUSIC : HIGGAION .(According to Gesenius, it signifies the murmuring tone of a harp, and hence that the music should be rendered in a plaintive manner.) .(Combined with "Selah," it may have been intended to indicate a pause in the vocal music while the instruments rendered an interlude.) (Psalms 19:14)