Snakes have the following traits.

Variable Size: See Table: Creature Sizes for attack and Defense modifiers based on size, as well as for a snake's fighting space (assuming the creature is coiled) and reach.

Improved Grab (Ex): Only constrictor snakes have this ability. To use this ability, a constrictor snake must hit with its bite attack. If it gets a hold, it can constrict (see below). See Improved Grab.

Constrict (Ex): With a successful grapple check against a creature of its size or smaller, a constrictor snake deals damage equal to its bite damage.

Poison (Ex): A viper injects venom with a successful bite. The victim must succeed on a Fortitude save or take 1d6 points of temporary Constitution damage. A second Fortitude save must be made 1 minute later to negate the venom's secondary damage (same as the initial damage). The save DC is equal to 11 + 1/2 the snake's Hit Dice + the snake's Constitution modifier (DC 11 for a Tiny viper).

Scent (Ex): This ability allows a snake to detect approaching enemies, sniff out hidden foes, and track by sense of smell. See Special Qualities for more information.

Skill Bonuses: Snakes receive a +8 species bonus on Balance checks and a +4 species bonus on Hide, Listen, and Spot checks. Snakes apply either their Strength or Dexterity modifier, whichever is higher, to Climb checks.

Bonus Feat: Vipers gain the bonus feat Weapon Finesse (bite).