…and also some women who had been cured of evil spirits and diseases: Mary (called Magdalene) from whom seven demons had come out… Luke 8:2

When the demons came out of the man, they went into the pigs, and the herd rushed down the steep bank into the lake and was drowned. Luke 8:33

            Sometimes when Jesus healed a person of demons, he encountered more than one demon inside the person.  Why was that?  Jesus said this about demons in Luke 11:

“When an impure spirit comes out of a person, it goes through arid places seeking rest and does not find it. Then it says, ‘I will return to the house I left.’ When it arrives, it finds the house swept clean and put in order. Then it goes and takes seven other spirits more wicked than itself, and they go in and live there. And the final condition of that person is worse than the first.”  Luke 11:24-26

            Demons like companionship and when they find an opportunity to work together, they seize it.  This makes them more effective.   This may explain why they fear Jesus who has the power to send them to the lake of fire, eternal damnation, which is a lonely place of separation.  They will not have any companionship there.