Sometimes, it is a hard nut to crack without an expert's help.

有时候，没有专家的帮助这是很难破解的问题。

In American English, the saying a hard nut to crack means something hard to understand.

在美式英语中，a hard nut to crack意思是很难理解的事情。

The Yankees were proving a hard nut to crack but they were cracking at last.

北方佬的确是个很难砸开的核桃，可是他们终于在破裂了。

The expression a hard nut to crack can also describe someone who is simply difficult to deal with.

a hard nut to crack这个表达也可以形容某人很难相处，应付。

This case was going to be a hard nut to crack.

这个案子本来就很难破解。

Or we simply do not know how to deal with them. So, we can say he or she is a hard nut to crack.

或者我们只是不知道如何去处理，相处。所以，我们可以说he or she is a hard nut to crack。

She's a bit of a hard nut to crack, so, uh, Simon and Natalie, you guys are gonna go down to the prison and talk to her. - Excuse me?

她有点难啃，那，西蒙和娜塔莉，你们到监狱去跟她谈谈。 -你说什么？