What are some film techniques and scenes involving rebellion in Metropolis?

Fritz Lang's 1927 masterpiece of silent cinema Metropolis, is often widely regarded as one of the finest films ever made. Released at the tail-end of the German Expressionist film movement, Metropolis utilized a wide range of cinematic themes, styles, and techniques that would later continue to be significantly influential for decades.
Metropolis takes place in a dystopian society in which a significant division of wealth separates (quite literally) businessmen from laborers. Classist dissent and economic equality serve as one of the film's primary themes. In what is perhaps one of the most famous and heavily studied scenes of the film, Freder—the film's protagonist and the son of the leader of Metropolis—watches as one of the city's factory machines explodes and kills several workers. Freder experiences a hallucination in which the machine becomes the Canaanite deity Moloch to which the workers are fed. This cinematic technique, which implements a touch of surrealism, creates a strong thematic metaphor of labor; quite specifically, the laborers are portrayed as sacrifices to a heartless and insatiable entity that perpetually needs to be fed.
As the film progresses, an android with the likeness of a woman enters the workers' area of the city, causing anger, dissent, and hatred among the crowds of workers. This android serves as a contrast to Maria, whose likeness the android had taken, who aims to bring the workers and businessmen together in peace. Lang's use of duality with these two figures shows two possible options of erasing the classist divide: peace and rebellion.
One technique, Lang's liberal use of extras (it's estimated that roughly 37,000 were used in the finished film), serves the purpose of showing the power of rebellion. With such a staggering number of workers in the rebelling crowd, Lang see
Other techniques, such as lavish set design and cutting-edge special effects, lent to the futuristic and dystopian style of the film. These techniques also assist in strongly implementing another of the film's themes: the danger and wearisome nature of technology and industrialism. This theme seems to inherently tie into the theme of the classist divide, for industrialism demands increased labor.
As a whole, Metropolis takes a peek into a dystopian future in which workers and businessmen are divided both economically and physically. Through technological cinematic advances, expressionist metaphors, and the use of a significant number of extras, Fritz Lang succeeds in creating a not-too-distant future in which class dissent leads to rebellion and violence.