Hideous Zippleback

The Hideous Zippleback is a large, two-headed dragon. It is sly and surprising, but certain noises can confuse it and cause it to entangle its heads.

Behavior
The dragon has two personalities and two minds, one in each head, and one often argues with the other head over what to do. This dragon reminds some Vikings of bickering siblings when they aren't running away from it. Occasionally the dragon forgets that it is a two headed dragon, and one head tries to go one way, and the other head tries to go the other way, this can be problematic. Even baby Zipplebacks fight over which direction to go or what to do.

Its two heads also can aid it in confusing its enemies. They have been known to creep up on a human and trap them between their two heads. They can also work together to catch prey (one head watches for danger while other watches food) or solve complex problems (one head scares prey into the mouth of the other). Due to their double heads, Zipplebacks have two brains, one in each head, and all four eyes simultaneously transmit information to both brains. If one head is covered up and food is stuck in front of the uncovered head, both heads will start salivating at the same time. Because of this, it is nearly impossible to sneak up on a Zippleback.

Abilities
With their two heads, the Zippleback is one of the oddest dragons in the world. However, its two heads also give it a deadly weapon that's unique from any other dragon species. The head on the right side breathes a green, flammable gas, while the left head produces an electrical spark from its mouth to ignite the gas, creating lethal explosions. By itself, the gas can make a human disorientated if inhaled.

They can also use this gas in order to hide themselves, which makes them very stealthy. They use it to unexpectedly strike their victims.

The Zippleback's special ability is to release a large amount of gas, and then set themselves on fire. They bite their own tails and become a flaming wheel, which they can use to knock out enemies.

In the movie, Fishlegs stated the Zippleback's venom effects the digestive system. However, the stats say that the Zippleback has no venom at all.

Despite the offical website claiming Zipplebacks are poor fliers and walkers, Zipplebacks have shown to be quite agile, fast, and have a large amount of stamina. This was demonstrated in the battle with the Red Death and later also multiple times in the series. Therefore, it is safe to assume that the Zippleback is actually a quite agile and flexible dragon, although nowhere being near the fastest.

Like most dragons, Zipplebacks have sharp claws and teeth that they use to attack enemies and catch their prey.

Weakness
The dual heads can be a vulnerability, as Drago Bludvist's forces were able to incapacitate a Zippleback by shooting darts into the neck of one head, knocking both heads out.

Appearance
The Hideous Zippleback is often described as one of the most unusual dragons in the world. This dragon has two long, serpentine necks with spikes on it. These spikes can 'zip' together, in order to create the illusion of one neck. At the end of the necks, are two short heads. The Zippleback has a large horn on its nose, and two thinner horns on top of its head. Like most dragons, they have yellow reptile-like eyes. The teeth in their lower jaw seem to be longer then the one's in the upper jaw, sticking out. They also have two tails, which can also 'zip' together. The end of the tail posses a fin-like structure on its tails. The official website stated that, thanks to its relatively short legs and wings, the Zippleback is a slow walker and flier. Despite this, Barf and Belch has been seen flying quite fast. Their legs possess short, but strong legs with four sharp claws. The Zippleback is probably one of the longest of the medium-sized dragons, if not the biggest.

Movie
In the film, Hiccup learns from Toothless that most dragons hate eels enough to actually fear them and uses this against a Zippleback to scare it back into its den during dragon training. At the end of the movie, a Hideous Zippleback (eventually named Barf and Belch) is flown by Ruffnut and Tuffnut. Each head seems to agree with one twin.

Description
The official website describes the Hideous Zippleback as follows: "Of all the dragons that inhabit our world, one of the most unusual and dangerous is the HIDEOUS ZIPPLEBACK. The Zippleback is one of the largest dragons you may ever encounter. It's unmistakable with its twin heads. The heads are distinct, with separate thoughts and different personalities. Like most dragons, Zipplebacks can fly, but their wings are small and they spend most of their time on the ground. Zipplebacks are solitary, preferring to hunt alone. They come out after sundown, prowling dark forests for victims. The attack of a Zippleback is like no other. Instead of breathing fire, a Zippleback makes explosions. One head BREATHES gas, and the other head LIGHTS it."

"This two-headed threat is the longest dragon and has the smallest wings & stubbiest legs. But the way it produces fire makes up for any physical drawbacks. While one head shoots out a flammable gas, the other ignites it with a spark -- allowing for attacks from long distances. “It is based more on a Siamese cat combined with a devious snakelike quality,” DeBlois says.

Trivia

 * Although the offical website states that the Hideous Zippleback is not effective in flight because of its smallHiedous_Zippleback_Concept2.jpg wings, during the young Vikings' counterattack against the Red Death in the movie, it's shown that the Zippleback (Barf and Belch) is agile, fast, and effective at flying.
 * It was believed that the Zippleback was unable to breathe gas and spark while in flight, but in the TV Series, Barf and Belch are seen to be more than capable to ignite and breathe gas without too much trouble.
 * The Hideous Zippleback resembles Zmey Gorynych, the Slavic Dragon.
 * The Hideous Zippleback's two heads working together is based on the proverb, "Two heads are better than Hideous_Zippleback_Concept1.jpg".
 * It's shown in a training addition to How to Train your Dragon (film) that Hideous Zipplebacks (and other dragons) have a sense of humor; when a Hideous Zippleback attacks Ruff and Tuff while the two twins fight, the heads grin at each other as the twins continue to fight dangling from the Zippleback's mouths.
 * The Zippleback is usually greenish, but the McDonalds promo toy is blue.
 * The dragon stats say that the Zippleback is non-venomous, but Fishlegs says otherwise, once commenting that its fangs can inject pre digestive venom into its victims.
 * The Zippleback's name is possibly derived from Zippo, a brand of lighter, which is fitting as one of the dragon's heads serves to light the gas produced by the other head. It could also be from zipper, as the dragon can link and unlink the spines on its neck and tail together.
 * To train a Zippleback, you must feed both heads at once, then play with the dragon.
 * Although this behavior was only seen once, when Barf and Belch approached Hiccup in the How to Train Your Dragon movie, they fanned out their wings, flapping them slightly and started aggressively hissing at him, which mimics the behavior of the Dilophosaurus in Jurassic Park when it fans out it's frill and growls to spit venom. This behavior is presumably done to make the Zippleback seem more menacing and larger than they appear. This display is never seen again.
 * Zipplebacks only need one rider in Wild Skies, How To Train Your Dragon video game and School of Dragons.
 * In battles, Zipplebacks have the secret ouroboros-like power to bite their own tails and set themselves on fire after spraying large amounts of gas, taking on the form of a flaming wheel that knocks down their opponents like ten-pins.