In a bilingual incantation written in both Sumerian and Akkadian, the god Asalluḫi describes the "evil udug" to his father Enki:

O my father, the evil udug [udug hul], its appearance is malignant and its stature towering,

Although it is not a god its clamour is great and its radiance [melam] immense,

It is dark, its shadow is pitch black and there is no light within its body,

It always hides, taking refuge, [it] does not stand proudly,

Its claws drip with bile, it leaves poison in its wake,

Its belt is not released, his arms enclose,

It fills the target of his anger with tears, in all lands, [its] battle cry cannot be restrained.

The udug is defined by what it is not: the demon is nameless and formless, even in its early appearances.

An incantation from the Old Babylonian Period (1830–1531 BC) defines the udug as: the one who, from the beginning, was not called by name... the one who never appeared with a form.