HUD Effect

Looking at Casltevania Lords of Shadow, an upcoming Hack n Slash game that borrows lots of features from other Hack n Slash games and looking to be phenomenon and promising. One feature the game possess that caught my eye was the HUD effect. It's the same effect heavily used in Metroid Prime in other FPS greatly lacks:/
Another game such as Republic Commandos uses this similar effect, though it's the only game I could get an example of how the HUD effect works.

So I was thinking what if Ninja Gaiden 3 uses this kind of HUD effect? how would it work? what would cause the effect?

Let's say everytime Ryu obliterates an enemy, blood effect will splatter on screen.

Ryu obliterates a Ninja and blood splatters on screen

Or we could just say everytime Ryu wipes off the blood on his weapon, the blood could virtually splash on the screen.

Again we may also add every time Ryu takes a damage, blood will start splashing on screen.