/// <summary>
/// 足跡スキル作動
/// </summary>
    private void useSkill()
    {
        GameObject.FindObjectOfType <GamePopupMessage>().SetMessage("スキル「嗅覚の覚醒」", 2.5f, GamePopUpColor.white);
        skillController.CoolDownToController();
        cameraAnimator.SetBool("usingSkill", true);
        AudioManager.Instance.PlaySEClipFromIndex(6, 0.6f);

        //レイヤー10(footprints)を追加
        mainCamera.cullingMask |= (1 << 10);

        //終了演出は1秒前から
        Observable.Timer(System.TimeSpan.FromMilliseconds(4000)).
        Subscribe(_ => skillAnimEnd());
        //スキル有効時間:5sec
        Observable.Timer(System.TimeSpan.FromMilliseconds(5000)).
        Subscribe(_ => skillEnd());
    }