Introducing new ferret question

Question
This is actually a follow up question to my original one, except the expert I received my first answer from, was maxed out by the time I got the answer! I understand you guys are extremely busy, and appreciate the time you take to answer our questions!

The summary is:
I introduced a new 4-5 month old female ferret to my established 2-3 year old bonded male and female. Male is doing fine with the newcomer, Ferra, but our female, Baby, and Ferra aren't quite getting along yet.

No one has pooped  in fear or drawn blood, but Ferra seems afraid of Baby.

So my follow up is this! Ferra has now started this new behavior when running around with our Baby. She runs to her hidey spot under the bookshelves and whenever Baby comes near, Ferra squeaks and almost screams at Baby and sticks her head out with an open mouth. No biting, just open mouths. Then of course Baby responds with her own open mouth. It's almost comical to watch, but I really wish I knew what they were doing. Is this fear and threatening from Ferra or something totally different?

I just want to understand the body language between them, so I can evaluate the situation and make sure I am handling this correctly. Does that make sense?

I desperately want them to get along, and think understanding their interactions will help!

Thanks so much!


Answer
Most ferrets can and will get along eventually. As long as there's no screaming, bleeding, or pooping during their encounters it's fine to assume they're getting along ok. As far as the open mouths are concerned, that's just a ferret's way to invite one another to play. It doesn't mean anything bad, it's just what they do when they're excited or playful. A low, drawn out hiss, on the other hand, is a sign to keep away. It's good that you're trying to pay attention to ferret language, you are well on your way to becoming an excellent ferret owner :)