Jesters could use their freedom in the court to intervene on behalf of others. In most cases this would mean interceding with the king to protect someone more vulnerable or hard done by, and to reverse an injustice.
This is a rare case of the jester stepping in to save the emperor himself. In an attempted assassination of an overweening minister, the tables were turned, and the Emperor faced having to drink his own poison.
The jester Shen Jiangao 申漸高 (Gradually Stretching Taller) rescued Southern Tang Emperor Liezu 南唐烈祖 (r. 937-42) from a brush with death. Unable to control the increasingly powerful Zhou Ben, Liezu invited him to a banquet and presented him with a goblet of poisoned wine. Ben suspected this and, pretending to be drunk, took the goblet intended for the emperor and poured half the poisoned wine into it, then knelt down and offered it, wishing him long life and suggesting that if he did not drink the same wine it would show there was no unity of heart and virtue between monarch and minister, and he could therefore not think of acceding to the emperor’s command.
This put Liezu in a `Catch 22′ situation:
The emperor’s face drained, a long silence ensued and he still did not speak. The courtiers did not know what to do and looked at each other, sweat pouring off them. The resourceful jester realized what was going on, and on the pretext of turning the whole thing into a joke, seized both cups and drank them, then whizzed out of the room. The emperor secretly sent a trusted courtier to him at his private residence, taking the finest medicines as an antidote, but to no avail – the jester’s brain burst and he died of a haemorrhage.
烈祖曲宴便殿，引鴆觥賜周本。本疑而不飲，佯醉，別引一卮，均酒之半，跪捧而進曰：「陛下千萬歲！陛下若不飲此，非君臣同心同德之義也，臣不敢奉詔。」上色變，無言久之，左右皆相顧流汗，莫知所從。伶倫申漸高，有機智者，竊諭其旨，迺乘談諧盡並兩盞以飲之，內杯於懷中，亟趨而出。上密使親信持藥詣私第解之，已不及矣，漸高腦潰而卒。
Source: Nan Tang jinshi 南唐近事, by Zheng Wenbao 鄭文寶 (953-1013), quoted in Youyuji 優語集, ed. & comp. Ren Erbei 任二北 (Shanghai: Wenyi Chubanshe, 1981; repr. 1982), p. 75.