public boolean isCollision(Sprite s1, Sprite s2) {
        // if the Sprites are the same, return false
        if (s1 == s2) {
            return false;
        }

        // if one of the Sprites is a dead Creature, return false
        if (s1 instanceof Creature && !((Creature)s1).isAlive()) {
            return false;
        }
        if (s2 instanceof Creature && !((Creature)s2).isAlive()) {
            return false;
        }

        // get the pixel location of the Sprites
        int s1x = Math.round(s1.getX());
        int s1y = Math.round(s1.getY());
        int s2x = Math.round(s2.getX());
        int s2y = Math.round(s2.getY());

        // check if the two sprites' boundaries intersect
        return (s1x < s2x + s2.getWidth() &&
            s2x < s1x + s1.getWidth() &&
            s1y < s2y + s2.getHeight() &&
            s2y < s1y + s1.getHeight());
    }