Snakes either have venom apparatus consisting of poison glands, ducts, and fangs for injecting venom, or they lack these features and are non-venomous. Venomous snakes have different types of fangs adapted for venom injection. The mechanism of biting involves a series of muscle contractions that erect the fangs and squeeze venom from the glands into the fangs. Venom is a complex mixture that can cause bleeding, organ damage, or paralysis depending on the snake species. Antivenom developed from horses immunized to snake venom can counteract the effects of bites.