What's the catch 的翻译比较灵活，依语境而定。日常交谈中，对方免费给你好处，常常反问：What's the catch?就是问“有什么诡计?”;也可译为“你这是什么意思?”或者“有什么内幕?”。因此，当美国人说"What's the catch?"时，他/她要表达的意思就是:"Any more information about it?"、"Can you give me more details about it?"。
Shirley: Our company is going to stage a party to celebrate the 10th anniversary of its foundation.
Jane: Great. What's the catch?
①It is said that the coming holiday is canceled.
②The sales manager is said to be suspended.
③The company went bankrupt overnight.
④ Unbelievable! Such a bum like him have been promoted.
1. anniversary n. 周年纪念
A series of movies will be shown to commemorate the 30th anniversary of his death.
He bought her a diamond ring on their tenth wedding anniversary.
She reproached her husband for having forgotten their wedding anniversary.
2. bum n. 懒鬼，流浪汉
The bum wore a tattered sweater and ripped pants.
John lost his job and went on the bum.
You're just a good for nothing bum!