‘And one of the crowd answered him, “Teacher, I brought to you my son, who has a dumb spirit, and wherever it takes him it dashes him down and he groans and grinds his teeth and is thoroughly exhausted, and I spoke to your disciples that they should cast it out, and they could not.”
A voice in the crowd answered Him. The voice was that of a father who had brought his possessed son seeking Jesus, and on not finding Him had probably been assured by the disciples that they could cast the spirit out. This is a sign of authenticity. No one would later invent the story of the failure of the disciples, especially after their previous success (Mark 6:13; compare Luke 10:17).
‘A dumb spirit.' Probably one that hid its presence by not speaking. It may also have made the boy dumb, but there is no indication of the fact. The actual description is somewhat similar to epilepsy but there is no question that had it been simply epilepsy or else the disciples would have been able to heal him. They had no doubt healed many epileptics. But here they were dealing with more than epilepsy, something that was beyond them, and in fact the details do suggest experiences deeper than epilepsy.
‘Is thoroughly exhausted.' The usual meaning of the word is ‘withered' or ‘dried up' (Mark 3:1; Mark 4:6; Mark 5:29; Mark 11:20). The unclean spirit was draining him of his very life.