Lord Buddha said that, we can't find origin point of creatures whose swaying in rebirth cycle (Sansara Crakra). Creatures are covered by unknowingness & bond to desires. Dependent Organism acts inside creatures for helps to rebirth. Four kinds of nutrition roots help to rebirthing: desires for foods we eat from mouth, mind impacts (consciousness + internal sensing organs + external masses), volition states (thinking from mind) & consciousness itself work as food. All these foods are - linking with desires of five senses, making like to rebirthing & creating dislike to rebirthing (such as disgusting about life). Creatures are wandering inside rebirth cycle as humans, animals, gods, hungry ghosts, demons, hell beings, etc. Lord Buddha said that it is good, if we can bear only human realms & heaven realms. But we can't control over our rebirthing because it decides by law of karma which made from dependent organism. If result made for rebirth in hell, we can't stop it when we die. Buddha said hell realms, animal realms & hungry ghost realms are like home to creatures. Creatures have possibility to rebirth in hell than human or heavenly realms. Our mind more attract to sins, bad habits & unskillful actions than merits & skillful actions. You can decide it by concerning yourselves such as you like to sleep, having sex & eat more than meditation or observe precepts. When you read details of hells, animal realms, hungry ghost realms & realms of demons (demons related to hell), think this way: how many life times I rebirth in such realms cause of my mistakes in rebirth cycle? Only Stream Enter & other higher states owned people can escape from all these four hells. Except that noble people, person who has steady devotion to Lord Buddha, also will not born in next life in hell or other low level realms, only born in heaven, so it also like as giving another opportunity to understand this enlightening path and then suggest to achieving it.
In Majjima Nikaya there has sutra called as Devaduta Sutra, which describes about hells in deep background. Devadutha means angles whose herald about hells. Lord Buddha see those hells & those creatures stay with pains from Devine-Eye which is some kind of supernatural power that Buddha had. In this sutra Buddha said "Bhikkhus, I say this not hearing from another recluse or monk, this is what I have myself known and seen and so I say it". In this sutra described about eight main hells but in Jataka Pali & Apadana Pali, there have briefly described about more 130 sub hells. Here we describe about main eight hells & how hell beings are get pains. Creatures existence in hell in form of astral body but has same organs as same as organs in human body such as muscles, blood vessels, skeletons, etc. So they can get same pains from burnings & cuttings. There have king related to hell who tries to escape creatures from hell even he or she rebirth in hell as Karma. His name is Yama. He ask five questions from hell beings mention about five angles: "early born baby, aged person, sick person, person who punished by government & finally death body", so his first questions is "Kindly Man, being a wise aged one, didn't it occur to you, I have not gone beyond birth, now I will do some good by body, words and mind?". If hell being can't give answers beyond these question by referring his good deeds were done by himself in human realms such as meditation, donations, observe precepts, etc. Finally king of hell said - "Good one, owing to negligence you acted in that manner. This evil action was not done by your, mother, father, brother, sister, friends, co-associates or blood relations. It was not done by recluses, monks or gods, it was done by you and you will experience its results". Then King Yama becomes silent, he don't say punishments, he only tries to escape being from hell because hell being was created punishments from himself via Karma. King Yama can escape creature from hell, if so only that being did good deeds in human world. As our researching, we found sometimes even only one little good action may help to escape from hell and then born in human world. But cause of the Karma, that person may suffer long-term illnesses due to his bad actions. So here are some experiences of hell & their painful punishments.
"Then the warders of hell give him the fivefold binding. That is two hot iron spikes are sent through his two palms, and two other hot spikes are sent through his two feet and the fifth hot iron spike is sent through his chest. On account of this he experiences sharp piercing unpleasant feelings. Yet he does not die, until his demerit finishes. Next the warders of hell conduct him and hammer him On account of this he experiences sharp piercing unpleasant feelings. Yet he does not die, until his demerit finishes. Next the warders of hell take him upside down and cut him with a knife On account of this too he experiences sharp piercing unpleasant feelings. Yet he does not die, until his demerit finishes. Next the warders of hell yoke him to a cart and make him go to and fro on a ground that is flaming and ablaze On account of this too he experiences sharp piercing unpleasant feelings. Yet he does not die, until his demerit finishes. Next the warders of hell make him ascend and descend a rock of burning ambers On account of this he experiences sharp piercing unpleasant feelings. Yet he does not die, until his demerit finishes. Next the warders of hell throw him upside down into a boiling, blazing pot of molten. There he is cooked in the molten scum, and he on his own accord dives in comes up and goes across in the molten pot. On account of this too he experiences sharp piercing unpleasant feelings. Yet he does not die, until his demerit finishes. Next the warders of hell throw him to the Great Hell."....."Parallel and together with the Hell of Excretes the Hell where hot ashes rain, he falls into that. There he experiences sharp piercing unpleasant feelings, yet he does not die until his demerit comes to an end. Parallel and together with the Hell where hot ashes rain, is the Simbali forest, more than seven miles tall, it has thorns sixteen inches long, aflame and blazing, he climbs on them and goes to and fro on them. There he experiences sharp piercing unpleasant feelings, yet he does not die until his demerit comes to an end. Parallel and together with the Simbali forest, is a forest of swords. He enters that. The leaves that fall with the wind, cut his feet, hands, feet and hands, ears, nose, ears and nose. There he experiences sharp piercing unpleasant feelings, yet he does not die until his demerit comes to an end. Parallel and together with the forest of swords is a huge salt water river He falls into that. In it he is carried up stream and down stream. There he experiences sharp piercing unpleasant feelings, yet he does not die until his demerit comes to an end." (From Sutra Pitakaya at metta.lk web site)
We can understand pains & unhelpfulness of animal realms. Animals can't take foods as they want, they can't talk, they can't take medicines when they got illnesses, sometimes small animals become foods stuff to other animals. Some animals always stay with fear. So there have untellable pains in animal realms.
Asura realms are widely described as group of gods but they do opposite actions against to “five precepts & ten skillful actions” such as they don't respect to monks, they make fear humans, influence to bad climate in earth, etc. These asuras are considered as demons but not as gods. They often live in astral houses in ocean. One groups are evil ghosts who have very long lifetime as even one Kappa & have extraordinary power such as make creations, kill someone from mind, destroy human life, etc. Other type of asura group is creatures between gods & devils. These are called as demons that have all power & luxury life as god but they eat human meat. They don't kill human being from effort but use tricky actions via cheating, such as people who are traveling in deserts see nice women & these women say there have village in desert so throw water. But there has no any water or village, these women are asuras who make tricky trap to kill those people in desert and then eat their meat. Those foolish people throw water tanks, then die without water in desert. So like these ways, asura beings are doing opposite actions against to “five precepts & ten skillful actions”. Therefore rebirthing in this realms also helps to gain sins & probably lost their merits then again drop down to hell or animal realms. Some asura are like hungry ghost, they have huge bodies such as mountain, sometime really attached to mountains, so without meals & water happen to stay about thousands of years. Some asuras have huge sex organs which is huge as heavy stones but their bodies are small, so they can't carry their body. They can't walk. These kinds of asuras are creating cause of laziness in human lifetime and wrong sexual relationships. We all have to do duty to mankind and universe, if we neglect those soul duties cause of laziness & sexual activities (wasting time only for sex), then we born in such asura realms.
After the hell, hungry ghost are the most painful creatures in rebirth cycle. They have very long lifetimes without food, cloths, water & they stay on excretes, mud, toilets, bath rooms, old dirty buildings, dirty homes, intersection roads, etc. Lot of times, they come into houses which is not maintain long time & not clean proper way. They like dirty smells such as urines. In Sutra Pitakaya, there have section related to them called Pretha Vaththu Pali. These ghost stories as same as modern ghost stories. However hungry ghosts are lucky than other hell creatures because some of them can gain merits while people transfer merits when they are doing good deeds. Hungry ghost also born as astral body. But their body can be seen by some human being. Some hungry ghosts have all luxury things same as gods but one essential thing is missing. As example some ghost have nice house with decorations & stay on lot of foods as heaven. But they don't have cloths. Hence they can't go out from their home. Here are examples of hungry ghosts in Pretha Vaththu Pali.
"Mother of Sariputhra arahant monk before five life times back, was born that hungry ghost who has very naked thin, skeleton, blood vessels shown body, who sleep in cemetery. She suffering from taste & hungry. She can't eat normal food stuff & drink water. Then she make her mind to eat excretes of human & animals, drink blood which drop from human & animal wounds, drink blood when youth girls got monthly sick, etc... When Sariputhra arahant monk transfer merit from donations to other arahant monks, she became as same as heavenly goddess."
"One wife of tailor became hungry ghost because she neglect her husband's Buddhist fellowship & blame him when he donate alarms to monks. She blame by telling to become those donations into excretes & urines, but after that husband die rebirth as god & wife rebirth as hungry ghost who can only eat excretes & urines." "Another two stores are one women rebirth as hungry ghost with face is like pig while body is like human because she didn't observe precepts via mouth. Other hungry ghost has upper path of body is like god with nice cloths but lower path of body is naked & spoiled cause when he was human he did bad actions from body."
"In Sanyuththa Nikaya had story about group of hungry ghosts who are same as Buddhist monks but their robes are burning cause in Kasapa Buddha's time they are Buddhist monks but didn't observe higher precepts."
In the Buddhist Cosmology, there have some kind of officers in universe such as King of Hell, Great Brahma, Sakkra God. As well as that “Bad One of Death” also such officer who bond creatures to rebirth cycle via figures, sounds, odors, tastes, body feelings & thoughts. In Pali language he is called as Papima Mara or Vasawarthi Mara (king of lustful bonding). As same as the god, person who did merit will rebirth as Mara king & people who did mere merits become his servants. Lord Buddha said Mara has most power except Buddha. Once time Maha Moggallana Arahant Monk also became as bad one of death in Kasapa Buddha's time, he also troubled that Buddha & arahant monks then as result of that sins he was born in hell. Wonderful factor is even Mara king have such great controllable power, after his merit powers are finished he born in hell. Lot of time Asuras are associated with Mara & his servants. Lord Buddha said when someone promises himself to achieve enlighten states such as Stream Entry, the Mara come close to him & disturbs him. Great persistence, precepts & concentration need to be neglect Mara & his troublesome servants.
After read these stories, we can conclude all four hell realms are very painful. If we decide to wander in rebirth cycle, we happen to go through hells, animal realms, hungry ghost realms & asura realms. Reasons to born in these realms are: accepting theory of soul, doubt about noble truths & bond to mere traditional activities which are removed from stream entry state. Only way to get rid from hells realms, animal realms, hungry ghost realms & asura realms is going on eight noble path & grow steady devotion to threefold refuge. So our main aim in this life must be enlightened into stream entering as real Buddhist person.