From Su Shi's (
苏轼) Song-dynasty poem 《
惠崇春江晚景》, inscribed on a painting by the monk Huichong:
竹外桃花三两枝,
春江水暖鸭先知 — 'Beyond the bamboo, a few sprigs of peach blossom; the spring river warms, and the duck knows first.' Today used almost exclusively as a metaphor for insiders sensing change.