The Duo Theory is the name given to the concept that there are two separate entities which rampaged through New York City, despite contradiction from J.J. Abrams, the movie, and the Cloverfield community.
In the movie Cloverfield, a giant monster attacks the city. As stated by J.J. Abrams, it is a baby. However, some believe it is not the only monster in the movie. They claim that another monster, possibly a parent or sibling, enters New York in an attempt to find and retrieve their kin.
- In the bridge scene, shortly before Jason's death, Hud looks forward in an attempt to see what the crowd is running from. He then records what appears to be the collapsing of the bridge, briefly followed by a fleshy object moving behind it. This is believed to be the mother monster. The tail that crushes the bridge is disproportionate to the size of the monster that is in the city.
- One distinguishing feature of the monster is its two front teeth, which portrude from its upper jaw even when its mouth is shut. The monster that eats Hud has a different appearance. Its front teeth jut out from its lower jaw.
- The monster that eats Hud appears to be considerably smaller than the one in the city, although it could simply be the angle from which it was filmed.