The following material is Open Game Content from the Menace Manual SRD
A hoop snake resembles an ordinary snake except that it has a head at either end of its body. It measures some 6 feet long and weighs about 75 pounds.
Constrict (Ex): A hoop snake deals bludgeoning damage with a successful grapple check against a target its own size category or smaller. The damage equals 1d6 + the snake’s Strength modifier.
Improved Grab (Ex): To use this ability, the hoop snake must hit an opponent at least one size category smaller than itself with its bite attack. If it gets a hold, it automatically deals bite damage each round that the hold is maintained, and it can constrict in the same round.
Poison (Ex): Bite—Fortitude negates; save DC 10 + 1/2 the snake’s Hit Dice + its Constitution modifier.
Scent (Ex): This ability allows a hoop snake to detect approaching enemies, sniff out hidden foes, and track by sense of smell.
Skill Bonuses: A hoop snake receives a +8 species bonus on Balance checks and a +4 species bonus on Hide, Listen, and Spot checks. It applies its Dexterity modifier instead of its Strength modifier to Climb checks.
Hoop Snake: CR 2; Medium-size animal; HD 3d8+3; hp 16; Mas 13; Init +5; Spd 40 ft.; Defense 16, touch 14, flat-footed 12 (+4 Dex, +2 natural); BAB +2; Grap +5; Atk +5 melee (1d6+3 plus poison, bite); Full Atk +5 melee (1d6+3 plus poison, 2 bites); FS 5 ft. by 5 ft. (coiled); Reach 5 ft.; SQ constrict 1d6+3, improved grab, poison (DC 12), scent; AL none; SV Fort +4, Ref +8, Will +2; AP 0; Rep +0; Str 17, Dex 20, Con 13, Int 2, Wis 12, Cha 2.
Skills: Balance +7, Climb +8, Hide +8, Listen +4, Spot +4.
Advancement: 4–5 HD (Medium-size); 6–12 HD (Large).
Advanced Hoop Snake: CR 4; Large animal; HD 7d8+21; hp 52; Mas 17; Init +4; Spd 40 ft.; Defense 17, touch 13, flatfooted 13 (–1 size, +4 Dex, +4 natural); BAB +5; Grap +16; Atk +11 melee (1d8+7 plus poison, bite); Full Atk +11 melee (1d8+7 plus poison, 2 bites); FS 10 ft. by 10 ft. (coiled); Reach 10 ft.; SQ constrict 1d6+7, improved grab, poison (DC 16), scent; AL none; SV Fort +8, Ref +9, Will +3; AP 0; Rep +0; Str 25, Dex 18, Con 17, Int 2, Wis 12, Cha 2.
Skills: Balance +6, Climb +12, Hide +3, Listen +4, Spot +4.