Alien Abduction: Incident in Lake County

The footage, interspersed with "expert" interviews, begins with the McPherson family gathered for Thanksgiving dinner. The power goes out, so Kurt and Brian go outside to check the fuses; Tommy follows with his camera. After finding the fuses charred and partially melted, they head into the woods to investigate a transformer which is throwing sparks.
They find a UFO in a nearby field. As they watch from the treeline, two aliens exit the ship and use a ray-gun on a cow. Despite their attempt to remain hidden, the three men are spotted. One of the aliens raises its weapon and burns Brian's hand. They rush back to the house and try to convince their incredulous family to flee while there is still time. They see lights in the sky and a furtive figure outside a window, but the family refuses to believe the brothers' story until Tommy plays them the tape. Suddenly, a high-frequency screech incapacitates everyone but five-year-old Rose. When it stops, Kurt straps a flashlight to his shotgun and decides to get everyone in his truck and leave.
The truck will not start. The battery has melted so they return to the house. As they take stock of the situation they hear scrabbling sounds from the roof and discover that an alien has made its way in through an open window. Kurt leads the way up the stairs and begins to search. Tommy takes the opportunity to go into his bedroom and change his soiled pants when he is ambushed by an alienâit (apparently) puts him in a trance, investigates his camera, and slips away, leaving Tommy with no memory of the encounter. Tommy is awakened by the shouts of Kurt, who has trapped an alien in an adjacent room. They are greeted by a laser shot and Kurt responds with his shotgun. Everyone retreats downstairs.
A ball of light floats into the house and puts Renee into a coma. Kurt and Brian go outside to try to swap out the truck battery in a final attempt to get the family to safety and take Renee to a hospital. Seemingly minutes after they leave, gunshots are heard outside and the lights begin to flicker. Those who remain experience a series of vivid auditory and visual hallucinations to which Rose seems to be immune. Tommy puts the camera down, and in a moment when she is left alone, Rose takes the shells out of the remaining shotgun. Later, everyone (except Rose) feels a burning sensation on the backs of their necks where they discover triangle-shaped burns.
The group becomes hysterical as more shots are heard. They go outside where Tommy discovers a couple of mangled shotguns, but not his brothers. The camera pans towards the woods to reveal strange lights and two approaching figures. Everyone races back into the house where they barricade themselves in. The camera is dropped and goes black. Tommy then gives a tearful testimonial and wonders if he will live to see tomorrow. He searches through all the rooms and suddenly comes face-to-face with an alien. Tommy drops the camera and stands frozen in a trance-like state. The tape stops. The family and their guests have not been seen since.
Alternate ending[edit]
An alternate ending is presented in an extended version of the film, made available after the initial television airing. In it, the family is seen re-entering the house and, after the death of Renee, the survivors gather around the table to eat in order to keep up their strength and spirits. It is implied that Rosie unlocks the front door because the aliens gain entry to the house and subdue the family with what appears to be psychic powers. An alien disables the camera as the family is seen following the aliens out of the house.

Question: Why does the group become hysterical?
Answer: Because they heard more shots fired.