'The Ambassadors' takes its figurative element from a photograph that appeared in many of the British tabloids some years ago. It shows a fight between some English and Turkish 'football fans'.
This photo shows the side view of the painting where you can see how the lines sheer off over the edge. The white line of the drawing is actually the primed surface showing through, so when you actually view the piece in the flesh, so to speak, your eye fluctuates slightly between the painted surface and the line drawing below. This can give the impression that the line of the drawing vibrates slightly.