记得中学时，班里曾有男同学手里拿着粉笔假装吸烟，还真蒙了不少人。仔细想想，粉笔和香烟还真是张得很像，只不过前者是消耗自己为人类服务，而后者是燃烧自己来危害人类。像这样外形相似，实质却大相径庭的例子无处不在，比如我们今天要说的chalk and cheese。

Cheese is soft and white; chalk is hard and also white. The words chalk and cheese are similar, as they begin with the same sound. Although chalk and cheese have such similarities¹, they are very different from each other in taste and texture², and this is the point made by this expression.

奶酪和粉笔都是白色的，但奶酪质软而粉笔质硬。它们的另一个相似点是两个单词chalk和cheese的开头音节都是ch，开头发音相同。虽然chalk（粉笔）和cheese（奶酪）有上述相似之处，但是它们的构成和味道却是完全不同的，这也是chalk and cheese这个短语意思的由来。

For example:

Although they are brothers, they are as different as chalk and cheese.

虽然他们是兄弟，但是两人一点也不一样。