A: The djinn have the capacity to take many forms and to change appearance. According to the Imam Ibn Taymiya, they can take a human or animal, form such as a cow, a scorpion, a snake, a bird.... The black dog is the devil of the dogs and the djinn often appear in this form. They can also appear in the form of a black cat.
When a djinn takes a human or animal form, it obeys the physical laws of this form; for example, it will be possible to see it or to kill it with a gunshot or to wound it with a knife. For this reason, djinn remain in these forms for only a short time because they are vulnerable. In fact, they benefit from their invisibility to frighten people.
Q: Are djinn both male and female?
A: Yes, there are males and females among the djinn. According to the Koran, the djinn have the capacity to procreate and can have offspring.
Q: Are djinn responsible for their acts?
A: Just like humans, the djinn are responsible for their acts. Indeed, Allah will take the day of the last Judgement to them.
According to the Imam Ibn Taymiya, the djinn observe obligations in relation to their specific nature. Being different from the human beings, their duties are inevitably different, too.
They have religious beliefs, too. Like human beings, they can be Christian, Jewish, Muslims, or non-believers. Some are pious, others are evil.
Q: Are djinn afraid of humans?
A: The djinn and men feared each other mutually, but the djinn were able to instill fear more intensely than men. The djinns are more fearful beings by nature, but they can also feel such human emotions as anger or sadness. In fact, the djinn benefit from these states, being better able to cause fear in the heart of man. Like bad dogs, when they sense your fear, they will attack.
For more information, see the Wikipedia article on Genie.