How do you convince your parents to let you get a pet rat?

I have done everything that I can think of to try and convince them, but they still say no. I have offered to pay for it, I have shown them pictures of them, I have told them all of the good stuff about them like how they are clean and that they are docile, among other things. If any one who has convinced their parents to let them get a rat, could you please share what really convinced them that rats make good pets?Oh, and when I ask her to give specifics, she has to reasons. Reason 1 is "because" and reason 2 is "because I said so". Any way to get past that?