The creature is very similar in appearance to the creature in Alien (1979). It attacks by grabbing onto the mouth of its victim before entering the victim's body. It bursts out of the chest of the victim. When the creature opens its mouth, another extension comes out of the mouth and opens its mouth.
Det. Ian McLemore:
Jerry, do you smell something?
Jerry Merris: Ah, smells like the old government cover-up.
(at around 55 mins) In the lab, just before the space object is drilled into, the lighting becomes substantially darker in the room between cuts (no doubt to increase the sense of fear), without anything to explain why.