“Seven, they are they seven,
In the deep they are seven,
Settling in heaven they are seven.
In a section of the deep they were nurtured;
Neither male nor female are they,
Destructive whirlwinds are they,
They have no wife, they produce no offspring.
Mercy and pity they know not,
Prayer and petition they hear not,
Horses raised in the mountains  are they.
Hostile to Ea  are they,
Throne bearers of the gods are they,
To hem the way they set themselves up in the streets.
Evil are they, evil are they,
Seven are they, they are seven, twice seven are they.”
Their universality as well as their function in seizing hold of their victims, taking up their seat in any part of the human body, is emphasized in another description.
More specific is the description of the demon Ti’u, the demon of head troubles and of fevers. 
“The head disease roams in the wilderness, raging like the wind,
Flaming like lightning, tearing along above and below,
Crushing him who fears not his god like a reed,
Cutting his sinews like a khinu-reed,
Maiming the limbs of him who has not a protecting goddess,
Glittering like a star of heaven, flowing like water,
Besetting a man like a whirlwind, driving him like a storm ;
Killing that man,
Piercing another as in a cramp, 
So that he is slashed like one whose heart has been torn out,
Burning like one thrown into the fire, 
Like a wild ass whose eyes are clouded, 
Attacking his life, in league with death,
So is Ti’u, who is like a heavy storm whose course no one can follow,
Whose final goal no one knows.”
Elsewhere the invisibility of the demons is dwelled upon. Of the Ashakku it is said  that, sweeping along like a storm, driving through the streets and highways
“He stands at the side of a man, without anyone seeing him,
He sits at the side of a man, without anyone seeing him,
He enters a house, without anyone seeing his form,
He leaves a house, without anyone observing him.”
Morris Jastrow, The Civilization of Babylonia and Assyria, 1915, pp. 243-4.