They must be getting scared that they will be attacked. This is a typical reflex response of someone that knows they are about to get there butts kicked.
See #5.
I’ve noticed an odd thing when two cats square off, (yes, cats, don’t disturb my analogy here) the cat that’s about to get it’s ass waxed makes a hell of a racket while the cat that’s about to apply the wax job just sits there and stares. OK, I know it’s lame but who’s doing all the yowling lately? Iran sure is making a hell of a racket.