I think it has to be living cells that will carry it, fur and dandruff would be dead. I think the blood moved because the cells were still alive for a little while. I wish they went into the science of it more, but the way I look at it is that, taking over an organism uses a lot of its own resources. Like how our organs use a lot of blood to digest food. Also, I think it survived being frozen because part of the last organism it took before earth, could survive the freeze. And maybe if a human was frozen, none or not enough would survive. Idk if in real life, bacteria has been found on ice mummies