Final monster design

A parasite that infests itself inside the human bone marrow, taking over how bones are formed forcing the hosts rib cage to break out of there chest and transform at a rapid pace into sharp spider like legs. These legs come to a point at each end that's sharp enough to impale a human, and thats just what they are build for. The strange growths half way down on the spikes are full of the parasite in its beginning form, so that when the spike is impaled through a host, the parasite can spread to create another one of these monsters.