Cinema only exists because of the way our eyes and brain work. When a series of images is run at speed, the eye cannot spot the gaps and the brain is fooled into thinking they are moving. Demonstrate this with a "flick book": draw a series of images in the corner of a notepad such as a person running. Riff the pages and the figure appears to move. When film projectors were hand-operated, projectionists occasionally cranked the handle too slowly; the gaps became noticeable, causing a flicker, hence the expression "going to the flicks".