Tiny black dots inside cell vacuoles - (Feb/28/2014 )

I am growing vero cells, and I noticed a cell that has two very large vacuoles.  I can see a bunch of tiny black dots rapidly moving around inside these vacuoles.  I have observed this for the past two days. No other cell in the flask has this.  I have no idea what it is. I don't have the ability to take a video of it, but I took a bunch of pictures and put it together in a time lapse video, magnification is 400x (40x objective, 10x ocular).  The vacuoles don't concern me, but I have no idea what is swimming around inside of them. Thoughts?

normally vero cells do not have vacuoles, unless you used too much fbs.  I'm not sure what those dots are, maybe not bacteria, because that could be just Brownian motion (google that) of some debris. Also, your cells are very confluent. you must not have them at that confluency or you might get more strange behaviour.