of the prey which their possessors may be in the act of swallowing.
Without such fangs escapes would be common; with such, they are rare.

"The natives of South Africa regard the _Bucephalus capensis_ as
poisonous; but in their opinion we cannot concur, as we have not been
able to discover the existence of any glands manifestly organised for
the secretion of poison. The fangs are enclosed in a soft, pulpy sheath,
the inner surface of which is commonly coated with a thin glairy
secretion. This secretion possibly may have something acrid and
irritating in its qualities, which may, when it enters a wound, occasion
pain and even swelling, but nothing of greater importance.

"The _Bucephalus capensis_ is generally found upon trees, to which it
resorts for the purpose of catching birds, upon which it delights to
feed. The presence of a specimen in a tree is generally soon discovered
by the birds of the neighbourhood, who collect around it, and fly to and
fro, uttering the most piercing cries, until some one, more
terror-struck than the rest, actually scans its lips, and, almost
without resistance, becomes a meal for its enemy. During such a
proceeding the snake is generally observed with its head raised about
ten or twelve inches above the branch round which its body and tail are
entwined, with its mouth open and its neck inflated, as if anxiously
endeavouring to increase the terror which it would almost appear it was
aware would sooner or later bring within its grasp some one of the
feathered group.

"Whatever may be said in ridicule of fascination, it is nevertheless
true that birds, and even quadrupeds, are, under such circumstances,
unable to retire from the presence of certain of their enemies; and,
what is even more extraordinary, unable to resist the propensity to
advance from a situation of actual safety into one of the most imminent
danger. This I have often seen exemplified in the case of birds and
snakes; and I have heard of instances equally curious, in which
antelopes and other quadrupeds have been so bewildered by the sudden
appearance of crocodiles, and by the grimaces and contortions they
practised, as to be unable to fly or even to move from the spot towards
which they were approaching to seize them."[170]

It may have been the Boomslange to which Le Vaillant alludes, who says
that he saw, on the branch of a tree, a species of shrike, trembling as
if in convulsions; and at the distance of nearly four feet,