Tang-dynasty Chan (Zen) master who struck his students with a staff to break their habits of thought. Paired with 临济's shout, his stick gave Chinese the idiom 当头棒喝, a sudden wake-up call.
Master Deshan was famous for the 'shout-and-stick' teaching method.
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An old woman selling snacks once stumped him with a pun on 点心 'snack', literally 'dot the mind': the 金刚经 he lectured on says past, present and future mind cannot be grasped, so which mind would he dot? After his awakening he burned his commentaries on it.