It's a group made of what I'm guessing is all kinds of species. As for their experiments, it can vary.

[Vash doesn't believe false sound of calm in Knives's voice. The last time Knives was here he hadn't taken that news very well either. Who really did? It was just not every new feather was as dangerous as Knives could be.]

Sometimes it's just the surrounding areas that will change. Sometimes it's easy to figure out what's going on, other times it's not so easy. The effects don't usually last more than a week or two.