Poison Spray, also called Acid Lash, is a skill used by Andariel in which she raises her left hand and swings it, throwing bolts of corrosive venom. Getting hit is almost always fatal, so Antidote potions are a must. Her mother, Lilith, also knows this fearsome ability.
Poison Spray spreads through the room, sending multiple bolts of Poison in several directions. Note that the poison is very potent; it will usually drain away all hitpoints in a matter of seconds. Bringing Antidote Potions should help mitigate this problem.