Mark 9:20
So they brought him. When the spirit saw Jesus, it immediately threw the boy into a convulsion. He fell to the ground and rolled around, foaming at the mouth — the spirit's violent reaction to Jesus' presence is the same pattern as in the synagogue exorcism (Mark 1:26): the demonic cannot approach Jesus passively but is thrown into violent reaction. The convulsion before the healing communicates both the reality and the intensity of the possession. The spirit is putting on its final display of power before being permanently expelled.