Corpsebomb

The fungus begins life as a tiny spore that floats along until inhaled by a creature, and lodges itself in the moist tissue of the lungs. The spore then begins to grow, causing irritation, pain, and finally death once the fungus has reached a sizable mass. Once the host creature has perished, the fungus increases growth rapidly until it pushes a hollow tendril forth from the flesh. At the exposed end of the tendril the fungus begins growing a thin membrane, which is inflated by the gasses produced by the rotting body.