The following material is Open Game Content from the Menace Manual SRD
Constrict (Ex): A giant anaconda deals 1d6+16 points of bludgeoning damage with a successful grapple check against a target at least one size category smaller than itself.
Improved Grab (Ex): To use this ability, the giant anaconda must hit an opponent at least one size category smaller than itself with either a bite or a tail slap attack. If it gets a hold, it automatically deals bite or tail slap damage each round that the hold is maintained, and it can constrict in the same round and attempt to swallow in the next round. If the giant anaconda wishes, it can continue to attack with its tail or its bite (not both) while it grapples with its body, but it takes a –20 penalty on all grapple checks if it does so.
Scent (Ex): This ability allows a giant anaconda to detect approaching enemies, sniff out hidden foes, and track by sense of smell.
Skill Bonuses: A giant anaconda gains a +8 species bonus on Balance, Climb, and Swim checks and a +4 species bonus on Hide, Listen, and Spot checks.
Swallow Whole (Ex): If a giant anaconda begins its turn with an opponent one or more size categories smaller than itself held in its mouth, it can attempt a new grapple check as though trying to pin the opponent. If it succeeds, it swallows its opponent, automatically dealing bite damage. Once inside the giant anaconda, the opponent takes bludgeoning damage equal to the anaconda’s tail slap attack plus 1d6 points of acid damage per round from the monster’s stomach. A successful grapple check allows the swallowed creature to climb out of the stomach and return to the giant anaconda’s maw, where another successful grapple check is needed to get free. Alternatively, the swallowed creature can attack from inside the stomach using claws or a Small or Tiny slashing weapon. Dealing at least 30 points of damage to the stomach (Defense 18) in this way creates an opening large enough to permit escape. Once a single swallowed creature exits, muscular action closes the hole; thus, another swallowed creature must cut its own way out. A Huge giant anaconda’s stomach can hold 1 Large, 2 Medium-size, 8 Small, 32 Tiny, or 128 Diminutive or smaller opponents.
Giant Anaconda: CR 9; Huge animal; HD 12d8+60; hp 114; Mas 21; Init +1; Spd 20 ft., climb 20 ft., swim 40 ft.; Defense 16, touch 9, flat-footed 15 (–2 size, +1 Dex, +7 natural); BAB +9; Grap +28; Atk +18 melee (1d6+11, tail slap); Full Atk +18 melee (1d6+11, tail slap) and +13 melee (2d6+5, bite); FS 15 ft. by 15 ft.; Reach 10 ft; SQ constrict (1d6+16), improved grab, low-light vision, scent, swallow whole; AL none; SV Fort +13, Ref +9, Will +5; AP 0; Rep +0; Str 32, Dex 13, Con 21, Int 1, Wis 12, Cha 2.
Skills: Balance +9, Climb +19, Hide +12, Listen +5, Spot +5, Swim +19.
Advancement: 13–23 HD (Huge); 24–36 HD (Gargantuan).
Advanced Giant Anaconda: CR 15; Gargantuan animal; HD 30d8+210; hp 345; Mas 25; Init +1; Spd 20 ft., climb 20 ft., swim 40 ft.; Defense 18, touch 7, flat-footed 17 (–4 size, +1 Dex, +11 natural); BAB +22; Grap +49; Atk +33 melee (1d8+15, tail slap); Full Atk +33 melee (1d8+15, tail slap) and +28 melee (2d8+7, bite); FS 20 ft. by 20 ft.; Reach 15 ft; SQ constrict (1d8+22), improved grab, low-light vision, scent, swallow whole; AL none; SV Fort +24, Ref +18, Will +11; AP 0; Rep +0; Str 40, Dex 13, Con 25, Int 1, Wis 12, Cha 2.
Skills: Balance +9, Climb +23, Hide +8, Listen +5, Spot +5,