Take a case where a certain individual looks just the same as other good-natured mendicants when going out and coming back, when looking ahead and aside, when bending and extending the limbs, and when bearing the outer robe, bowl and robes. That is, so long as the mendicants don’t notice his offense. But when the mendicants notice the offense, they know that he’s a corrupt ascetic, just useless trash. When they realize this they send him away. Why is that? So that he doesn’t corrupt good-natured mendicants.

Suppose in a growing field of barley some bad barley appeared, just useless trash. Its roots, stem, and leaves would look just the same as the healthy barley. That is, so long as the head doesn’t appear. But when the head appears, they know that it’s bad barley, just useless trash. When they realize this they pull it up by the roots and throw it outside the field. Why is that? So that it doesn’t spoil the good barley.