“Whenever it seizes him,
It dashes him down.
He grinds his teeth.
He becomes rigid,
καὶ ὅπου ἐὰν αὐτὸν καταλάβῃ, ῥήσσει αὐτόν, καὶ ἀφρίζει καὶ τρίζει τοὺς ὀδόντας καὶ ξηραίνεται·
The story of the man with the incurable son can be found in all 3 synoptic gospels, Matthew, chapter 17:15, Luke, chapter 9:39, and here in Mark, but there are minor differences in all 3 accounts. Apparently, this son was an epileptic, who was often considered to be possessed by the devil. Even today, we are still unsure of the exact cause of epilepsy seizures. This description of the young man’s suffering differed from Matthew who had the child suffer very badly, falling into fire and water. Luke had a description similar to Mark. However, this was a very descriptive narrative of what was happening to this young man. Mark said that whenever the spirit seized him (καὶ ὅπου ἐὰν αὐτὸν καταλάβῃ), it dashed or threw him down (ῥήσσει αὐτόν). This young boy would foam (καὶ ἀφρίζει) at the mouth. He would grind or gnash his teeth (αὶ τρίζει τοὺς ὀδόντας). He would become rigid as he was wasting or withering away (καὶ ξηραίνεται).