PacMan 0.4 is a strange PacMan game. When coding the game, the programmer has to create a logical maze where the monsters and the PacMan move into. So, when I type an arrow, the program has to see if the movement is permitted or not, according to the point where the PacMan is, in the logical maze.
In the original game, the logical maze (the structure in the memory of the computer that is used by the game to process the player movements) coincides with the maze that is showed in the screen. In PacMan 0.4, the logical maze doesn't coincide with the "visual maze." But the game still works: you can move inside a maze, the only thing is that it is not the maze that is showed for you. You can eat food, and you will get points eating food. You can also lose a life, when a monster touches you.