These creatures look like men and women, clad in a strange armour. This 'armour' may really be part of their bodies. They have no heads, instead posessing a flattened block which somewhat resembles a cinema screen.
They are known for their treatment of the dead of other races. They are said to drill into the brains of the corpse (the drill may be part of their armour, or of their bodies), and extract something. The superstitious insist it is the soul of the deceased, but the learned reply that they do this to corpses long-dead, whose soul would have flown long ago.
In any case, the treatment causes their 'head' to show an image of the dead person, as they were in life. Some have claimed that it speaks, showing knowledge that only the dead person could have. Others claim that the head tries to give this impression, but in reality gives general observations that could apply to anyone, or repeats information they glean from observation. This 'face' seems to last for months or years, but eventually to fade.
They are said by some to be aggressive, having a need to kill in order to make their strange harvest. Others dispute this, and say that they are attacked due to the horror that they provoke, and only defend themselves. Yet others claim that their behaviour is a merciful freeing of trapped souls.
Their reputation for aggression may partly come from their reaction to the death of one of their own. Should its face-screen have been blank, they show no emotion. But if it had a 'face' they seem to be utterly dismayed, and run howling in all directions. In either case they will return, and perform some activity which none have seen, which removes all evidence of the corpse. Should they be observed they will carry the corpse elsewhere. They will retrieve the corpse of one of their own at all costs, and seem to have an unfailing ability to know that such exists. If an entire group is killed, others will eventually arrive for them.