S.T.A.L.K.E.R. CoP: Bloodsucker in sights

Hard to see on this picture, but generally you want to stay on a good distance from a bloodsucker, since the flakkers are hella fast when running and - most importantly - can go freaking INVISIBLE (In CoP they go invisible only when they spot the prey, not when startled, while in ShoC they were cloaked all the time bar attacking and in CS they also were INVULNERABLE in that mode, but in CoP they got an instakill chance). They are still somewhat visible (blank white eyes, air distortion) up close and uncloaked when attacking. Still the best solution is to snipe the bastard (ideally, with a Gauss Rifle). If already spotted, always watch your back, and keep the shotgun ready.