As far as I am concerned, the evidence is unverifiable. I am not convinced by the paint brush theory. If you watch the video, the part that - to my understanding - is being called a handle appears to be formed rather than having existed throughout the entire clip. Whatever it is seems to draw back, forming a tendril that loops around to briefly create the shape of a (somewhat thick and cartoonish) brush handle.
The substance doesn't move like I think paint would. It pulls into itself and it's trail seems much too clean. And if you look at the front of the large solid orb portion (before it zooms downward) you have to assume that it must be pressed against something to create the tail tendrils. The problem is that the tail tendrils are much smaller than the width of the alleged brush. The stroke should be much wider. Maybe you could trim the bristles down at an angle, but I think if this was done you would see more bristle patterns along the front and sides or the bulk of the "orb" would be smaller or it would be very awkwardly shaped rather than forming a relatively thick circular pattern. Plus trimmed bristles would likely leave behind messy droplets.
And when it moves, you see it pull back, loop over and head down. If you watch, you can make out an almost solid shape (created by the sudden back and down looping motion of the main mass). Yes, I realize you might see that from paint on a brush (or some other oozing type material) but if you notice, the shape remains even after the bulk of the main mass (what would have to be the bristles) has passed over it. If this was paint for example, that would not have held its shape. It would have been smeared and would leave a smear trail all the way down.
And, if this was just light reflecting off of something intentionally, then wouldn't the brush handle that you insist is very clearly visible also be reflected and appear as part of the mass? The middle should reflect as well if it is solid, so we should see a big white arm for at least part of the clip while the brush is preparing to make its descent. Instead the middle is black, as if it is hollow (meaning there is no handle there).
Finally, the object moves like a single mass pulling itself together. You get the sense that it is some what solid but still made of a set amount of mass because it literally pulls itself back down. Paint doesn't really collect itself. It might shrink and thin out and smear, but I think that this substance is not messy enough and a little too orderly to be something on a brush.
And, as was mentioned, there is the issue of no visible arm, string or other support that would be needed to hold and guide the brush (which would be a tricky task if one end was weighted down with wet paint or some other thick liquid).
I could be wrong and I'm not 100% convinced there isn't a hoax behind this yet. This is just my uneducated opinion but it is for these reasons that I am reluctant to jump on the bandwagon made of paintbrushes.
