As I understand it, jinn can become physical beings, for some indefinite period of time. During this time period, they may or may not act in line with the normal behaviors of creature they are mimicking. So in theory, any given animal or person could be a jinni.
What are the criteria that I can use to test if someone or something is actually a jinni?
There is no such thing as a test to figure out whether something is a jinn. There is nothing of the sort in Quran or Hadith or anywhere else.
Proof?
In the conditions of Marriage, there is no requirement that you must test your bride to see if she is human.
In the conditions of Halal Zibah and Hunting, there is no requirement that you must test the animal to see if what you are about to kill and eat is anything other than what it appears to be.
If such a test existed, it would have been prescribed in the conditions of the above.
First to fix some of the comments that are wrong here, can jinn take the form of a human? Yes they can. Can they take the shape and form of an animal? Yes they can. But they only become human if they want to hurt someone or say something to someone if you want to get rid of them i mean if you find one that is after you read ayet al kursi and it will burn them if it is an animal i am not sure but for a snake say alsalam alaikum 3 times then swear to god if they dont come of their hiding place you will kill them if the snake comes out dont touch it and leave if it does not come out its safe for you i hope that answered your question.
Proof down
Jinn are assumed to be able to appear in shapes of various animals such as cats, owls and onagers. Serpents are the animals most associated with jinn; in Islamic tradition, many narratives concern a serpent who was actually a jinni. The term jann refers to both a snake and jinn.
Abu as-Sa'ib, the freed slaved of Hisham b. Zuhra, said that he visited Abu Sa'id Khudri in his house, (and he further) said: I found him saying his prayer, so I sat down waiting for him to finish his prayer when I heard a stir in the bundles (of wood) lying in a comer of the house. I looked towards it and found a snake. I jumped up in order to kill it, but he (Abu Sa'id Khudri) made a gesture that I should sit down. So I sat down and as he finished (the prayer) he pointed to a room in the house and said: Do you see this room? I said: Yes. He said: There was a young man amongst us who had been newly wedded. We went with Allah's Messenger (to participate in the Battle) of Trench when a young man in the midday used to seek permission from Allah's Messenger to return to his family. One day he sought permission from him and Allah's Messenger (after granting him the permission) said to him: Carry your weapons with you for I fear the tribe of Quraiza (may harm you). The man carried the weapons and then came back and found his wife standing between the two doors. He bent towards her smitten by jealousy and made a dash towards her with a spear in order to stab her. She said: Keep your spear away and enter the house until you see that which has made me come out. He entered and found a big snake coiled on the bedding. He darted with the spear and pierced it and then went out having fixed it in the house, but the snake quivered and attacked him and no one knew which of them died first, the snake or the young man. We came to Allah's Apostle and made a mention to him and said: Supplicate to Allah that that (man) may be brought back to life. Thereupon he said: Ask forgiveness for your companion and then said: There are in Medina “Jinns” who have accepted Islam, so when you see any one of them, pronounce a warning to it for three days, and if they appear before you after that, then kill it for that is a devil.
(3) Sunan of Abu Dawud, Book 41, Number 5236:
Narrated Abu Sa'id al-Khudri:
Muhammad ibn Abu Yahya said that his father told that he and his companion went to Abu Sa'id al-Khudri to pay a sick visit to him. He said: Then we came out from him and met a companion of ours who wanted to go to him. We went ahead and sat in the mosque. He then came back and told us that he heard Abu Sa'id al-Khudri say: The Apostle of Allah said: Some snakes are jinn; so when anyone sees one of them in his house, he should give it a warning three times. [4521]. If it return (after that), he should kill it, for it is a devil.
The answer to this is that it is proven in the sunnah (prophetic teachings) and from real life that the jinn appear in different forms, such as the forms of people and animals, etc. Among the clearest evidence of that from the sunnah is the story narrated by al-Bukhari from Abu Hurayrah (may Allah be pleased with him) who said: The Messenger of Allah (peace and blessings of Allah be upon him) put me in charge of guarding the zakah (poor-due) of Ramadhan. Someone came to me and started scooping up some of the food, and I said, “By Allah, I will take you to the Messenger of Allah (peace and blessings of Allah be upon him).” He complained of being in need and having dependents, so Abu Hurayrah (may Allah be pleased with him) took pity on him and let him go. This happened three times, and on the third occasion, Abu Hurayrah (may Allah be pleased with him) said: “I will take you to the Messenger of Allah. This is the third time and each time you say that you will not come back, then you come back.” He said, “Let me go and I will teach you something by means of which Allah will benefit you.” I said: “What is it?” He said: “When you go to bed, recite Ayat al-Kursi, ‘Allah! La ilaha illa Huwa (none has the right to be worshipped but He), Al-Hayyul-Qayyum (the Ever Living, the One Who sustains and protects all that exists)…’ [2:255] until you complete the verse, then you will always have a protector from Allah, and no devil will come near you until morning comes. So I let him go, and the next morning I told the Messenger of Allah (peace and blessings of Allah be upon him) what had happened. The Messenger of Allah (peace and blessings of Allah be upon him) said: “He told you the truth, although he is a liar. Do you know who you have been speaking to for three nights, O Abu Hurayrah?” He said: “No.” He said: “That was a devil (a shaytan).”
Jinn can't "become physical beings" per se, and by "physical" I presume is meant creatures that humans can perceive and have a tangible existence. Rather they inhabit or "possess" physical beings, which in this case would not mean "own" but "take over". Thus it is that they can also be cast out or exorcised by an Imam or Sheikh trained in doing this and who should have strong faith and a strong personality to withstand the difficulties involved. There are specific protocols, including the reading of specific ayat from the Quran a specific number of times, as well as other things to be said.
As to how one can "identify" a case of possession, usually the victim, who should have been previously normal and without mental or behavioral issues, suddenly or gradually takes on abnormal behaviors which would always be negative and destructive. They would tend to steer away from Islam and salat if they were Muslim, to treat family and friends with hostility, isolate themselves, and also engage in self-destructive behavior. Physical manifestations could include speaking in an abnormal voice or voices, acting out with violence, using profanity, and sleep disturbances such as nightmares. It is the combination of all of this into a noticeable and frightening trend that clearly identifies the victim as a potential case of possession.
As for animals, a possessed animal would act violently against people, but this is not a definitive matter because animals can act that way for many other reasons. Jinn are interested in harming people, not animals, so the point of taking over an animal would be to terrify and harass people.
So it is not true even theoretically that "any animal or person can be a jinn." The Quran mentions some people as being Satanic, but this is due to their bad behavior reaching a point of no return, not jinn possession. They are referred to as "shaiateen al-ins" or "satans in human form." They are humans who have so committed themselves to evil that they seek to destroy others' lives as well and work on Satan's revenge as an avowed enemy of humankind. Of course, such people are their own worst enemy.
