Morphing (Mutation):
Technique that consists in gradually transforming one image into another.
Widely used (and easy to implement) in stop motion, the plasticine is gradually deformed, and enriched with new elements until it reaches the desired result.
An example of this are both motion pictures in stop motion, and many special effects, including those of films such as "The Evil Within", which witnessed the metamorphosis of human becoming demons.
With video the process is analogous, but assisted by the computer: points of interest on the first image are created, corresponding to as many points of interest on the second image, and the computer creates the transition between the two images.
In 3d, the process is more like in the traditional stop motion: we create an object composed of an X number of vertices. It is duplicated, and deformed, being careful to keep the same number of vertices.
At this point an intercalation process can be created between the first object and the second one.
Technique in this case very used in special effects, or simply for the animation of the expression or the lips of the animated characters.
