Strata-cut animation is a common a form of clay animation in which long bread-shaped hunks of clay are packed in layers that create an image. The artist cuts the clay in succession to create animations. It's hard to describe but you will understand once you watch the video below. It is a difficult medium because not only are you thinking about the X,Y, and Z axes of the work, but time also contributes to your work.
David Daniels is an artist who has been doing this kind of work for years. Below are videos of his greatest hits and now that you know how its made, you can appreciate all of the hard work and time he put into his projects. It may surprise you that some of his works may be familiar.