Pretty much what the title says, a Zombie that has been infected as a conjoined twin. Basically one head would be the "infected" side and controls the body while the other head is alive but suffering. The living side would scream at you and yell to warn you and try to save you (Could also raise threat level due to noise), maybe even sometimes asking for release from the horrible fate that has sadly taken them. This could be a really freaky and rare enemy type and maybe replace Child zombies potentially?
Gameplay wise I think the model should be wide and this zombie should be the "tanky" type. Requiring more to take down but slow. Or maybe make it so if you shoot one head the other is still alive, so you could potentially need to destroy BOTH brains to kill it. But Killing the "living side" alone doesn't do anything but shut the living head up. I'm not sure on specifics but the idea itself could make sense and add some real horror the the situation of the virus. Showing that anyone can be affected, even those with physical defects.
Lets expand on this idea and try to pin down a version of this that would work for this game down below, I'm super interested to see how ya'll would polish this idea up.