Tóunǎo fēngbào de shíhou, shénme xiǎngfǎ dōu kěyǐ tí.
During a brainstorm any idea is fair game.
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Calque of English 'brainstorm': 头脑 (head/brain) + 风暴 (windstorm/tempest). Also commonly used as a verb: 我们头脑风暴一下 (Wǒmen tóunǎo fēngbào yíxià, 'let's brainstorm for a sec').
