The hair of the dog 

In English, when we say 'the hair of the dog', we mean a small alcoholic drink which you have to cure a hangover. It's just an expression.

The hair of the dog 就是喝点儿酒来解醉，以毒攻毒。

不过这个短语也够怪的，为什么用狗毛来表示解醉酒？

那是因为it comes from the phrase 'the hair of the dog that bit me'. It's a reference to a medieval belief that when someone was bitten by a dog with the disease rabies, they could be cured by putting the same dog's hair onto the infected wound.

例句：

A: I went out last night and knocked back a few too many drinks.
B: Let’s go to the pub. You need the hair of the dog.