open up
verb
Definitions
To open.
Example: Open up the door!
To reveal oneself; to share personal information about oneself; to become communicative.
Example: After three hours of questioning, he finally opened up.
To commence firing weapons.
Example: As the convoy entered the pass, we opened up on them with everything we had.
(of the sky) To rain.
Example: The sky has really opened up. I've never seen this much rain!