Welcome to Wireworld. In Wireworld space is discrete. It consists of cells, arranged in a grid.
Cells come in four "states", which are from left to right: Black, Copper, Electron head and Electron tail.
Not only space, but also time is discrete in Wireworld. Although cells never move, they may change their state from one point in time to the other.
Black cells always stay black.
Electron tails become Copper.
Electron heads become Electron tails.
And finally a cell in Copper state switches to Electron head state if one or two of its neighbours are in Electron head state. Copper cells with three or more cells in Electron head state remains in copper state.
Sounds pretty boring, doesn't it? Let's take a look at the bigger picture.
Keep in mind that movement is illusion in Wireworld!