For anybody who does not know what a zebiba is, it is the mark found on the forehead of some Muslim men and is caused by repeated bashing of the forehead on the ground during prayer. It is often seen as a mark of great piety and devotion, and in many Muslim communities is a highly respectable thing to sport.
However, there are links between damage to this part of the skull and the onset of psychopathic tendencies. It is believed by a number of neurologists to affect a person's moral compass, as in severe cases it removes what we would refer to as having a 'conscience'.
It is interesting to note that some of the most passionate of 'hate preachers' are known to have a prominent zebiba and this 'mark of the beast', so to speak, is found on a number of those convicted of acts of terrorism too.