The fact the movie leads with a title card reading "...retrieved from the area formerly known as Central Park." ::shudder::
They're not revealed in the film itself, but you see those tube-like things dangling from Clover's belly? According to behind the scenes material, those are essentially elongated mouths with teethlike fingers that lead into Clover's stomach. Anyone unfortunate to be running underneath them are sucked up and eaten alive. Imagine running for your life, only be sucked up by those things. Or even worse, imagine running with your family, only to watch them get sucked up.
The exact fate of Marlena. While the main characters are walking through a Sinister Subway tunnel, a scene which is pretty creepy in its own right, Marlena gets bitten by one of the parasites that fall off of the giant monster-thing. A few minutes later, when they end up at a first-aid center set up by the Military, her eyes start bleeding uncontrollably. Everyone starts freaking out, they drag her behind a curtain and we see a huge splatter of blood against it. We explicitly see her body rapidly blow up like a balloon and explode.