Demons are one of the known inhuman entities out there. Fortunately, they are a rare occurrence.
They are usually very easy to identify as long as they are not hiding. When it is a demonic haunting you typically notice a revolting stench similar to rotted flesh or sulfuric acid. They often let loose a growl that sounds like it is coming from everywhere at once. They like to make contact by pushing, shoving, hitting, and even scratching. The whole air in the affected area will feel thick like fog and the temperature will drastically change, typically becoming warmer.
These creatures are very strong, unlike human spirits, and they don't mind showing it. There have been cases where people have been thrown through the air and even attacked. Apparently, their main goal is to break down a person's free will in order to make way for possession. This can take days, months or years, but time is of no concern to them.
They have a hatred for mankind that dates back to the days of God and Lucifer. They have lived for millennia and will be here long after we are gone. So, you must understand that though you may be able to get these creatures to leave a dwelling with religious provocation you will never destroy them. They could go to the next place down the road if they choose, most likely they won't because distance is not a problem for these creatures. They could go from Maine to California on a thought.
They can take on any form they wish, but mostly commonly it is a half man, half animal form. They will have the head of an animal, the torso of a man, and the hairy legs of an animal. When they are approached by an investigating paranormal team they may feel threatened and appear in a human form to keep the home from being blessed and stop the use of religious provocation.
During an investigation you need assess the situation more by what happened before you arrived than what is actually going on during the time you are there. Demons are capable of changing form right in front of you from a human form to an inhuman form. They neither male nor female, but then can change that to meet their needs. People mostly see demons as black masses standing in doorways or near rooms. Sometimes they are called shadow devils.
If you feel like you have a demon in your home I would recommend getting help from a well known paranormal group as quickly as possible. Time is of the essence when dealing with these creatures.
