int x = 0;  int y = 0; int xspeed = 5; int yspeed = 2; int size = 50;

int mouth = 0;

void setup(){  

  size(640, 480);

}

void draw(){

  background(0);

  if(x > 320){

    fill(255, 255, 0);

  } else {

      fill(255, 255, 255);  

  }

  if(mouth++ % 10 < 5){

    arc(x, y, size, size, radians(30), radians(330));

  } else{

    arc(x, y, size, size, radians(5), radians(355));

  }

  x = x + xspeed;

  if(x > 640  ||  x < 0) {

    xspeed = xspeed * (-1);

  }

    y = y + yspeed;

  if(y > 480  ||  y < 0) {

    yspeed = yspeed * (-1);

  }

}