The Little Shop of Horrors

Seymour, a flower shop assistant (and milquetoast), acquires a plant named Audrey Jr. that starts growing at an incredibly fast rate. It soon develops other unusual traits, such as a voice and an insatiable appetite for human blood. As a result, the plant not only becomes gigantic, but it verbally bullies Seymour, who is forced to find ways to acquire human blood to feed his "pet." (official distributor synopsis)