Switching Images

//in your counter class;

//you need to import some classes to use this code:
import java.util.List;

//also you need another global variable;
private boolean imagesSet = false;

//in this example counter is the current number of the counter that is displayed and imageSetNumber is the number that has to be reached to change the images of the animals;
//imagesSet is a boolean to check whether the images already been set so you don't set them every act;
public void act() {
    if (!imagesSet && counter >= imageSetNumber) {
        imagesSet = true;
        //instead of Animal you have to use the classname of the objects you want to set the image of;
        List<Animal> animalsInWorld = getWorld().getObjects(Animal.class);
        for (Animal animal : animalsInWorld) {
            animal.setImage(new GreenfootImage("filename.png"));//here you have to add the right filename of your new image;
        }
    }
}

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class Snake here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Snake extends Mover

{
  private int score = 0;
  private GreenfootImage image2 = new GreenfootImage("Snake2.png");
  private GreenfootImage image3 = new GreenfootImage("Snake3.png");
  
  public void act()
  {
 score = score + 1;
if( score == 5 ) {
   setImage( image2 ); 
} 

}
}

public Snake(int score)
{
    if (score < 5) ; // use default image (do nothing)
    else if (score < 15) setImage(image2);
    else setImage(image3);
}

if (canSee(Snake.class))
{
    eat(Snake.class);
    score++;
    getWorld().addObject(new Snake(score), someX, someY);
}