[Cbprf]

Too tired to read through all the posts so I don't know if someone has already said this, haha, but from my experience and what I have read on other sites, it can also be used to let you know they're annoyed with something. My does did it when I introduced them to each other, but they eventually stopped once they got used to one another, and now my two new ones do it also because they're not quite used to the others.

 

[Cbprf]

Oh and I wanted to add, my new one who does the tail flit isn't a dark color. She's a creamy grey, so maybe it's not just the darker furred ones? Whatever, either way... mine did it out of annoyance due to the new cage mates but eventually stopped.