a hidden drawback or disadvantage 诡计, 圈套, 陷阱; 隐藏着的问题或缺点; 难人的问题； 蹊跷
Free food? It sounds too good to be true. What's the catch? 免费食物？听起来难以置信，有什么条件？
That new car is very cheap; there must be a catch in it somewhere!
那辆新车这么便宜,里面一定有蹊跷!
That question looks easy, but there's a catch in it.
那个问题看起来容易，但这里面有蹊跷。