If they start shooting we'll hit them back hard.

如果他们开始射击 我们会猛烈还击。

Snape gripped the back of a chair very hard and said, How can you be sure?

斯内普紧紧地抓住一把椅子的椅背，问道：“你怎么能肯定？”

His back hit the back of the chair hard.

他的后背重重地撞在椅背上。

He told the Associated Press, " It was harder back then to make people aware, show that everyone would benefit."

他对美联社说，“当时很难让人们意识到这个项目可以让每个人都受益。”

" God, " she said, and put the back of her hand hard against her mouth.

“上帝啊，”她说，用手背捂住嘴巴。

Another reason is a thousand-page encyclopedia with a rigid hard back would hurt a bit if you were hit over the head with it.

另一个原因是， 一本千页的百科全书， 硬硬的后背，如果被它击中头部， 会有点痛。