There are bacteria that infect halos, when angels remain for too long on
Earth. Slowly you see it creeping over that thing like the mange on an old
statue left out in the garden. Sometimes an angel has to have a halectomy,
and while this is not painful, it's rather disconcerting to the patient, who
is given an ankh to clutch during the procedure -- something like the strop
of leather you give to a man when you must cut off his leg in wartime. The
ankh is not for biting, however, but for holding in the hand as a temporary
eternifying device until the halo itself, a circle representing true
eternity, is completely regenerated.

This explains the Egyptian gods in representation. Some scribe witnessed
angels one day in the midst of this procedure -- he'd lost his way in the
fields of mfkzt, at the portals of Amenthes, and and found himself in one of
the many hospitals described in OAHSPE as ministering to those in the
afterlife who require spiritual healing. He rounded the corner and espied the
patients on the lawn, like customers of rustic english barbers -- he only
caught a brief glimpse before being shoved out of range by a matronly angel
with a gigantic bosom.

So impressed was he by these ankhs that he quickly jotted the information
down on a piece of wet clay...one thing led to another, then, as with all
things representative, soon became a stereotype.