The Frog don't move

private Animator playerAnimator;
private float moveHorizontal;
private float moveVertical;
private Vector3 movement;
private float turningSpeed = 20f;
private Rigidbody playerRigidbody;

// Use this for initialization
void Start () {

    // Gather components from the Player GameObject
    playerAnimator = GetComponent<Animator> ();
    playerRigidbody = GetComponent<Rigidbody> ();

}

// Update is called once per frame
void Update () {

    // Gather input from the keyboard
    moveHorizontal = Input.GetAxisRaw ("Horizontal");
    moveVertical = Input.GetAxisRaw ("Vertical");
    movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);

}

void FixedUpdate () {

    // If the player's movement vector doesn't uqual zero...
    if (movement != Vector3.zero) {

        // ...then create a target rotation based on the movement vector...
        Quaternion targetRotation = Quaternion.LookRotation(movement, Vector3.up);

        // ...and create another rotation that moves from the current rotation to the target rotation...
        Quaternion newRotation = Quaternion.Lerp (playerRigidbody.rotation, targetRotation, turningSpeed * Time.deltaTime);

        // ...and change the player's rotation to the new incremental rotation...
        playerRigidbody.MoveRotation(newRotation);

        // then play the jump animation.
        playerAnimator.SetFloat ("Speed", 3f);

    } else {

        // Otherwise don't play the animation
        playerAnimator.SetFloat ("Speed", 0);

    }

}