Beep.

It is known by every hero, when in action their legs move before the brains can even process the information.
Beep.
But what if, the same applies for villians?
Beep.
They just kill someone without thinking?
Beep.
All instinct?
Beep.
Adrenaline powered.
Beep.
And no mercy. What then?
Heartbeat Flatline Sound.