Hakuin used to tell his pupils about an old woman who had a teashoppraising her understanding of Zen. The pupils refused to believe what he told them and would go to the teashop to find out for themselves.
Whenever the woman saw them coming she could tell at once whether they had come for tea or to look into her grasp of Zen. In the former caseshe would serve them graciously. In the lattershe would beckon the pupils to come behind her screen. The instant they obeyedshe would strike them with a fire-poker.
Nine out of ten of them could not escape her beating.