It came from space.
Near the end of the movie they played the end of the video camera taping of the couple a month before spending a day at Coney island. In the footage you see something like a comet falling from space and into the ocean. I heard them say on camera, "It's probably a satellite." But that was the alien turd and it took itself a month to incubate and grow.
Infected people exploded.
When their friend was bit and they took here to the back of the quarantine only to explode.
It wasn't killed in the end of the movie.
If you stay till the end credits, you'll hear a radio transmission, It's still alive!" Perfect set up for the sequel!!!!!
