Q: A secret only you two know?
 

Jungkook: If I say it, then it won’t be a secret anymore. It’ll be big trouble if I talk about it. It seems like there’s nothing I can say.

Jin: What are you talking about (laughs) If there’s something I want to keep a secret then I won’t tell anymore. My mouth has been locked up since the beginning (laughs).

MY THEORY:

Now. 

For jinkook, jungkook's answer is clearly suspicious.Don't
even try to deny it. I mean they just normally answered
with other members.

But why is kookie holding back and jin just responded accordingly?
THEY DIDN'T TELL US ANYTHING AT ALL.