曲突徙薪

客有過主人者,見其竈直突,傍有積薪。客謂主人更為曲突,遠徙其薪;不者,且有火患。主人嘿然不應。

俄而家果失火;鄰里共救之,幸而得息。於是殺牛置酒,謝其鄰人;灼爛者在於上行,餘各以功次坐,而不錄言曲突者。

人謂主人曰:「鄉使聽客人之言,不費牛酒,終亡火患。今論功而請賓,曲突徙薪亡恩澤,燋頭爛額為上客耶?」主人迺寤而請之。

Sheep in Scotland

A mathematician, a physicist, and an engineer are riding a train through Scotland.

The engineer looks out the window, sees a black sheep, and exclaims, “Hey! They’ve got black sheep in Scotland!”

The physicist looks out the window and corrects the engineer, “Strictly speaking, all we know is that there’s at least one black sheep in Scotland.”

The mathematician looks out the window and corrects the physicist, “Strictly speaking, all we know is that is that at least one side of one sheep is black in Scotland.”

Ref: http://www.cs.northwestern.edu/~riesbeck/mathphyseng.html