Artist Neville Page designed this alien with a biological rationale for it in mind, even though many of his ideas (elongated and articulated external esophagus) did not appear on screen.
Its movements represent an immature creature suffering from separation anxiety, recalling real-life elephants that get frightened and lash out.
In the climax of Bryan Yuzna’s film, a high school student learns that his family and their high-society friends are actually a different species. To demonstrate, wealthy party guests strip to their underwear to literally feed on the poor, physically deforming and melding with each other.
What the student does to one of the monsters during a fight is best left to experience for yourself.