Christ asks the scribes what they are questioning the disciple about; he challenges them but their answer is not recorded. Before they can answer someone in the crowd intervenes.
The demon took him; he foamed, gnashed his teeth and then collapsed. Before conversion, we are not demon possessed but we are in the grip of the tempter. This event is not an exact picture of the unconverted state, but it is a sketch; there are many parallels. The demon possessed are constrained to do as the demon wishes. As unconverted people, we do as we are tempted; we sin willingly, but inevitably. We follow the fashions; we want to run our own lives. This case is a picture of anyone the devil controls. He was made to act against his own interests; he was thrown into the fire. That too is true of the unconverted. You constantly acting against your own interest to destroy yourself eternally, but that is not how we see it. Instead of finding meaning, purpose, we are unstable. We don’t have any principle of life driving us. We don’t have profound moral principles to guide us. We see ourselves as only here to enjoy the present moment. This boy was cut off from the world, and could not communicate; nor can we communicate with God. Also notice he was beyond the help of ordinary people, and similarly even top doctors cannot help in matters of the soul.
Matthew's Gospel uses an interesting word. He calls him ‘a lunatic’, which translates the Greek which means something like moonstruck, but it doesn't necessarily mean that ‘lunatic’ is the correct term to use, because this moonstruck term can be used quite generally. In Matthew's Gospel it is used as part of a precise description of an epileptic. So the lunatic word takes on the epileptic symptoms and sense. When Matthew calls him a moonstruck boy, he means that in very general terms. It's the term be uses for an epileptic boy. And those are certainly the symptoms described in Mark's Gospel.