About the phrase: "...and cross-check."

The announcement to "cross-check" means flight attendants with responsibility to arm their respective doors are to verify that the door on the opposite side of the plane has indeed been armed. They are to check this immediately after they arm their own door. It's a bit of redundancy that was added to the procedure of arming the doors sometime in the eighties. I'm not sure if the "cross-check" directive is an FAA regulation or if it's a procedure that airlines have picked up from each other.

I'm not sure how it is supposed to work in 747 upper decks. If I'm not mistaken, I think that some of the configurations have doors without a door exactly opposite, so cross-checking doesn't happen. But it was certainly someone's responsibility to arm the door.

Good eye, Droneklax. You double-cross-checked!