Catch 22 / Catch of the day / What's the catch?

catch-22 [beco sem saída] is a paradoxical situation from which an individual cannot escape because of contradictory rules. An example would be: To apply for a job, you need to have a few years of experience. But in order to gain experience, you need to get a job first.

Catch of the day refers to a fish caught within the last 72 hours or the fresh fish shelf life (usually 72 hours) that has not been frozen, canned or otherwise

What's the catch? (Qual é a pegadinha? O que está por trás?)
"OK, I've seen all the benefits, but what's the catch?"
"The restaurant is offering free lunch, but what's the catch?"