Jerkiness

Note 1: The perception of continuous motion by human vision faculties is a manifestation of complex functions, i.e., characteristics, of the eyes and brain. When presented with a sequence of fixed, i.e., still, images of sufficient continuity and at a sufficiently frequent update[?] rate, the brain interpolates intermediate images, and the observer subjectively appears to see continuous motion that in reality does not exist.

Note 2: For example, the update rate of NTSC television displays is 30 frames (60 fields) per second.

Source: from Federal Standard 1037C