______________ became a possibility when people realized that flipping through pages of related pictures produced the illusion of movement. Each variation of the image on each page, is slightly different then the one before, which creates the illusion in our mind.

Film became possible when people recognized that a sequence of slightly different pictures, viewed quickly, creates the illusion of movement. This is the same principle used by a flipbook, so the correct choice is Film. Sound and panning shots do not create motion from a sequence of still images.

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