The car pursuing Mac drives over some spikes, and comes to a complete stop with the wheels practically on top of these spikes. However, with no time passing between cuts, the car has instantly moved forward so that the spikes are not in view.
When Mac and the girl drive away from the cemetery, Mac puts his sun glasses on as the car starts to move, then as the camera angle changes suddenly his glasses are gone, and we see him put them on a second time.
How did Piedra know who his target was ment to be? and why did he continue his assasination attempt if he didn't get paid?