Anti-gravity depleted uranium bats

So, these genetically-engineered mutant bats have a wingspan of two or three feet and a body about the size of a small cat. And yet the force of a high-speed collision knocks a fully grown adult human flat on his or her back. Therefore they must have a very much greater mass than one would expect. Also, they are the result of weapons research. Conclusion: the bats are made of depleted uranium.
However there's no way those wings could keep that much mass airborne. Conclusion: antigravity-equipped bats.

And thus one deduces the existence of anti-gravity depleted uranium bats. Or, possibly, merely the existence of an extremely bad film.

imdb on "Bats"