Each cell represents a person with one of two "opinions." One opinion is represented by "." and the other opinion is represented by "M".
Each cell has 8 neighbors - 4 "near neighbors" to the north, south, east, and west, and 4 "far neighbors" at the 4 corners. If a cell's neighbors all have the same opinion as the cell, then the cell has no reason to change its opinion, and there is 0 probability that the cell will change its opinion.
For each of the near neighbors with a differing opinion, the probability that the cell's opinion will change at the next step is increased by 0.1. For each of the far neighbors with a differing opinion, the probability that the cell's opinion will change is increased by 0.05. So, for example, if a cell is entirely surrounded by neighbors of different opinion, there is a probability of 0.6 that the cell will change its opinion at the next step.