Liquid is the classical state of matter with a definite volume but no fixed shape.
cats are liquid
This animation of falling sand was created by defining 16 simple rules [shown below] about how the sand ought to behave in 2×2 grids. Breaking up the problem makes it easy to simulate the complicated patterns of falling sand. Systems which define rules on a grid like this are called cellular automata. Other famous examples include Conway’s Game of Life.