The "head" of the snake continually moves forward, unable to stop, growing ever longer. It must be steered left, right, up, and down to avoid hitting walls and the body of the snake.
In the game of Boa, the player uses the arrow keys to move a snake(brownish red square) around the board. As the snake finds food, it eats the food(cream colored square), and thereby grows larger. The game ends when the snake either moves off the screen or moves into itself. The goal is to make the snake as large as possible before that happens.