Barf and Belch

"What we can't get you is another Barf and Belch" - Hiccup to the twins.

Barf and Belch is the male Hideous Zippleback owned and trained by Ruffnut and Tuffnut. Barf and Belch are like their owners, they have trouble which head goes what direction and focusing on one target. However, unlike Ruffnut and Tuffnut, they can work together and find their owners annoying with their constant bickering.

Personality
Barf and Belch have the personality of a normal Zippleback; however, they have a laughable sense of humor. They enjoy doing the tasks Ruffnut and Tuffnut tell them to do, but they are in constant quarrel because of the fact that they have to listen to two different commands they are unable to do. Barf and Belch often get annoyed with their riders constant bickering, but are willing to protect them at any costs. For example, when Torch first approached Tuffnut as an adult, they were willing to fight him in order to protect Tuffnut (Zippleback Down) and they left the cave that they were supposed to stay in during Astrid's harsh training session to find Ruffnut who they felt was in danger (The Night and the Fury).

Appearance
Barf and Belch have the apperance of a normal Zippleback. Despite the head's resemblance towards each other, there are minor differences that each head has. Barf has a slightly curved horn as opposed to Belch's horn which is straighter. Barf's longest teeth are in the back of his jaw and Belch has his longest teeth in front of his jaw. Barf's skin is also slightly more lighter than Belch's. The skin color and tooth differences disappear by the time of the second movie (from what has been seen in images, this is most likely a production goof).

How to Train Your Dragon (Movie)
Barf and Belch were one of the captured dragons used to train the Viking Teens. The lesson they taught was to work together to find the head that lit up the gas (which was Belch). Later, Hiccup manages to get Ruffnut and Tuffnut to bond with them in time to help defeat the Red Death.

At the climax of the film, Ruffnut and Tuffnut, along with the rest of the Viking's teens, were on dragons. They helped the twins distract the Red Death to allow Snotlout and Fishlegs to attack them. By the end of the movie, the twins are seen riding Barf and Belch along with the other Viking Teens.

Riders of Berk
It was revealed in the show that the left head's name is Barf and the right is Belch, with Ruffnut apparently commanding Barf while Tuffnut controls Belch.

In the episode In Dragons We Trust, Barf and Belch are framed by Mildew of the crime of stealing all the boots of the village during "boot night," sleeping in a bed of boots. They are then proven innocent by the comparison of their tracks and the tracks at the scene, noting how their tracks are deeper.

In Twinsanity, Barf and Belch briefly went rogue after Ruffnut and Tuffnut's conflict with each other reached a point where they were issuing contradictory orders to the head they controlled, the Zippleback roaming around the village just as renegade Viking chief Dagur the Deranged arrived to discuss a treaty. Wishing to sign the treaty in dragon's blood, Dagur captured and nearly decapitated Barf and Belch, but the twins were able to reconcile in time to help their dragon escape, the other dragons faking an attack on the training ring to conceal Berk's new trained dragons in order to avoid provoking war.

Defenders of Berk
Barf and Belch appear in almost every episode, appearing alongside or being ridden by the twins.

In the episode, Zippleback Down, they accompanied the twins as they attempt to dislodge hidden traps. When Tuffnut was captured, they were ordered by Ruffnut to watch over her bother while she attempted to go get Hiccup so he could free her brother. Although annoyed by Tuffnut's constant efforts to start a conversation with them, they end up playing with him (though Tuffnut didn't enjoy it much). They tried to protect Tuffnut when a wild Typhoomerang (Torch) aggressively approached him. Defending Tuffnut, they are caught in a bola-string trap, but they manage to cause a big enough explosion to start a forest fire somewhere off. They were freed by Hiccup when he arrived on Toothless and they rode Torch. The Zippleback ended up helping to put out the forest fire and arrived back home on Berk safely on Torch's back. Later that night, when Ruffnut fails to free her brother from the trap and ended up with both of them being trapped, they leave their riders to bicker to presumably return home.

In View to a Skrill Part I and Part II, Barf and Belch helped to free the Skrill from the ice block, along with Snotlout and Hookfang.The twins rode them and they helped to snuff out the Skrill from the clouds so Hiccup could knock it down. They manage to save Hiccup from being blasted by lightning, although the twins and them ended up being chased themselves. Barf and Belch manage to land safely on an outcrop of land in the middle of the ocean and helps the twins go after Alvin. Later they are seen  on Outcast Island being watched over by Ruffnut as Tuffnut and Hiccup tried to gather information about them. They appeared again later to help seal up the hole, trapping the Skrill in ice once again.

How to Train Your Dragon 2
Barf and Belch briefly appears being ridden by their riders, Ruffnut and Tuffnut. Barf in particular shows annoyance and slight aggressiveness when Snotlout approaches Ruffnut to flirt with her.

Skills and Ablities
Barf and Belch seem to have the normal abilities of a regular Zippleback, although some of their abilities and gain skills are heightened due to training under Ruffnut and Tuffnut have shown them.

Strength: Barf & Belch are seen to be able to lift up heavy objects with their claws. Both claws can lift up a weight of 2 heavy grown adult Vikings: Like weight is 400lbs Stoick and Gobber unknown weight. Their riders though it was two fully grown Yaks not Vikings. They were also able to avoid being dragged off the roof by Toothless and stood their ground in the episode Twinsanity, showing that they might be physically stronger than a Night Fury. Their neck muscle have shown to be strong to carry the weight of Fishlegs on their neck in the air showing no sign of struggle. Also Barf showed that he can make Fishlegs jump off on Meatlug. They can lift in their mouth as well like they lifted up the weight of berserker easily to threw them away.

Jaw Strength: They have shown to have powerful jaws but can hold back their full strength this was shown when Belch bit down on Ruffnutt to give her little pain enough to please Tuffnutt.

Acrobatics: This is seen in the battle against the Red Death, when they manage to avoid sudden bursts of fire by the Red Death with agility also having a flexible body they can twist their necks and tails. Their heads are flexible enough to be upside down easily and their tail is flexible enough to be put front of their heads. They have shown great reflex by backing off their long necks from attacks.

Speed: Barf and Belch were also able to catch up with the Skrill in View to a Skrill Part I, although the Skrill had been slowed down slightly by Stormfly and Toothless.

Gas and Spark: Barf has the ability to release a large amount of gas at once (as seen in View to a Skrill) and still be able to release gas afterwards (but he soon reached his shot limit). Both Barf and Belch are able to create an exploding fireball, the only dragon, other than Toothless, in the Academy who doesn't breathe fire. Several times during the TV Series, it has been stated and shown that Barf's gas can cause whoever breathes it in to be disoriented and/or confused, as well as feeling sick. The twins are the only ones who don't seem to be affected by it.

Synchronization: Barf and Belch have the ability to synchronize their actions, similar to how Ruffnut and Tuffnut do. They work together when their riders are in trouble and always seem to know what the other head is thinking; however, they occasionally fight. When not fighting they will do the headbutt on each other like their owners do when they are happy

Intelligence: Barf and Belch are as smart as an average Zippleback. They always know when their riders (Ruffnut and Tuffnut) have gone too far in fighting and often take charge if they are in trouble. Though sometimes they fight with each other after seeing their riders fight. They also know hand-signals, as well as obedience to their respective riders. Occasionally, they will disobey or misunderstand their rider's commands. Though their intelligence have shown they can mess up like they will think on their when belch was releasing a lot of gas to make the Skrill to come out barf was going to spark to early so Tuffnut have to tell him not yet while Belch wants to blast.

Communication Skills: Like all Academy dragons, including Torch, Barf and Belch are trained in the basics of hand signals. Although, Barf will only obey Ruffnut's hand-signals and Belch will only obey Tuffnut's hand signals. Barf has learnt "gas", "go", "fly",and "attack". Belch has learnt "come", "down","bite", "drop", and "fly". Both heads seem to understand their owners talking about to agreed.

Endurance and Stamina : Barf and Belch have great endurable body that shown to be able to withstand attacks from a Typhoonmerang strength (as seen in Zippleback Down). That were still be able to stand and fight. As well as being blasted out of the sky and still managing to land on a outcrop of land  to protect the twins from getting hurt (View to a Skrill Part I).

Fighting Style: They shown to fight like average Zippleback like Barf and Belch uses a series of large explosions most battles using their Gas and Spark ability. Other times, they are seen using their heads and tails to do a series of quick jabs and headbutts to knock away opponents, mostly at Vikings or small opponents. Only very rarely do they use their teeth to bite opponents, the only known time was when Tuffnut ordered Belch to "eat" Ruffnut in the episode, Twinsanity. Although seen with large claws, they haven't been seen attacking with them.

Loyalty: They have shown to be very loyal to their owners and always help out their plans to do tricks and pranks. Barf is loyal to Ruffnut and Belch to Tuffnut. Barf is also seen to help Tuffnut and Belch to help Ruffnut, meaning both are willing to protect both twins from harm no matter what.

Rescue Skill: Unlike the other dragons were taught to save Vikings they were train to not help and watch. So the riders won't get hurt.

Trivia

 * Barf and Belch were originally supposed to be ridden by Fishlegs, but he briefly rode on Barf in Twinsanity after the dragon flew away without the twins, along with Snotlout, who rode on Belch
 * While the dragon is male, Barf and Belch are commonly referred to as "them" or "it," most likely due to the two heads being individuals. The only episode where they are referred to as "he" is Dragon Flower.
 * So far, Barf and Belch is the only one of the Academy dragons that Hiccup hasn't ridden at least once.
 * Barf and Belch are the only known Zippleback that has riders, this might be because you need two of them, in this case, Ruffnut and Tuffnut.
 * In the How to Train Your Dragon Movie, when they were approaching Hiccup, Barf and Belch spread their wings and start hissing, which is similar to the behavior of the Dilophosaurus in the movie, Jurassic Park. Barf and Belch are never seen to do this again.
 * They seem to chase their tails when they are bored.