void OnCollisionEnter2D(Collision2D col)
    {
        score--;
        aM.explosion();
        Destroy(col.gameObject);
        ContactPoint2D contact = col.GetContact(0);
        Quaternion     rot     = Quaternion.FromToRotation(Vector3.up, contact.normal);
        Vector3        pos     = contact.point;
        GameObject     exp     = Instantiate(explosion, pos, rot);

        exp.transform.eulerAngles = new Vector3(0f, 0f, exp.transform.eulerAngles.z + 180f);
        exp.SetActive(true);
        cam.backgroundColor = Color.Lerp(deadSky, startColor, (1f * score) / startScore);


        switch (score)
        {
        case 8:
        case 6:
        case 4:
        case 2:
        case 0:
            Destroy(transform.GetChild(0).gameObject);
            break;
        }
    }