Single frames from 'Tween Frames

Thinking about animation the most important feature seems to be the construction of motion by creating from 12 up to 30 frames per second; the amount of pictures needed to deceive the eye and still let images appear to be moving in our perception. Therefore each single frame of a time-based-recording is the logical result as well as the link of the previous frame and the following one. But while "Frame 2" is the only logical connection between "Frame 1" and "Frame 3", it is in particular the physical "law of nature". However, what would it look like if that "Frame 2" were replaced by another linking image, to be precise by a computer generated connection.

As a result, both of them indeed are "correct" in the end, but still - natural motion underlies different rules than mathematically calculated computer transformations. But what are the those differences? And particularly what would they look like? What would a process of replacing images by computer morphs change in our visual perception of moving images? The film evolves from replacing every other frame to changing almost every frame and just leaving some few remaining original keyframes.