Caustic Adaptation
(Underdark, page 24, DnD 3.5)
[General]
Long have your ancestors hunted and been hunted in the depths. Natural selection has given your blood an unpalatable, acidic quality.
Prerequisite
Kuo-toa
Benefit
A creature that makes a successful bite attack against you takes 1d4 points of acid damage. Creatures immune to poison are not affected.