The term ``migration'' probably got its name from some association with movement. A casual inspection of migrated and unmigrated sections shows that migration causes many reflection events to shift their positions. These shifts are necessary because the apparent positions of reflection events on unmigrated sections are generally not the true positions of the reflectors in the earth. It is not difficult to visualize why such ``acoustic illusions'' occur. An analysis of a zero-offset section shot above a dipping reflector illustrates most of the key concepts.