What does it mean when a girl shakes her butt?

[Greateye]

Why would she do that out of nowhere?

Did she wanted attention?

Context:

I'm with a friend having a conversation entering a room. We find this girl that we've known for a year. My friend found her in the corner of the room she started to goof around with her. A part of goofing off that was unusual was that she slightly bent over, she had shaken her butt and raised one of her arms in the air while doing this at the same time. Me and my friend said and commented:"that was out of nowhere" and all three of us were laughing as well. It makes it weird because it's the first time she's done this at all and she hasn't done this in all the time I've known her.

In my case, I've known this girl for a year but communication hasn't been the best. At the beginning she would talk to you often but the encounters were every 3 - 4 times a month (so it was tough during those times because these conversation barely lasted 5 minutes.

[SSJBrutus]

She farted and is trying to wave the stink away. Or maybe she has a wedgie and this is how she gets rid of it without picking it out of her buttcrack.