If Harry could only enter, unseen, behind him, what might he not see or hear？

这个问句属于修辞性问句。否定的问句形式实际表示强烈的肯定。

因此，what might he not see or hear?= he might see or hear everything.

原翻译没理解修辞性问句，对问句部分的翻译是错误的。另外，if...only为只要。。。

正确译文应为：

只要哈里能跟在他后面进去不被发现，他有什么看不见或听不到呢？

与刘老师讨论

刘老师对修辞性问句的理解有些狭隘了。请读一下夸克书中的以下内容：

夸克《英语语法大全》（英文版）P. 825-826

Rhetorical questions

11.23 The rhetorical question is interrogative in structure, but has the force of a strong assertion. It generally does not expect an answer.

A positive rhetorical yes-no question is like a strong negative assertion, while a negative question is like a strong positive one.

POSITIVE :

Is that a reason for despair? ['Surely that is not a reason. . .']

Can anyone doubt the wisdom of this action? ['Surely no one can doubt. . .']

NEGATIVE :

Isn't the answer obvious? ['Surely the answer is obvious.']

Haven't you got anything better to do? ['Surely you have something better to do.']

… …

There are also rhetorical wh-questions. The positive question is equivalent to a statement in which the wh-element is replaced by a negative element:

Who knows/cares? ['Nobody knows/cares' or 'I don't know/care.']

What difference does it make? ['It makes no difference.']

How should I know? ['There is no reason why I should know.']

What should I say? ['There is nothing that I should say.']

What makes you think you can do better? ['Nothing should make

you think you can do better.']

How can I help it? ['There is no reason why I can help it.']

Non-assertives may occur:

What has he ever done for you?

Who has any money to spare these days?

The less common negative question is equivalent to a statement in which the

wh-element is replaced by a positive element:

Who doesn’t know? ['Everybody knows.']

How couldn’t you remember? ['You certainly should have remembered.']

因此，我对句子的理解和翻译是正确的。您的理解不符合该句的语境。原翻译忽视了if...only，只要。。。就。。。同时也忽略了修辞性问句的否定形式表示肯定的意义，而二者是呼应的。只要。。。肯定就。。。怎么会是普通的问句呢？刘老师再想想。