Why can't I instantiate prefabs when I press "S"

I follow mentor in code live but when I press S, I can't create dogs like them

 public GameObject[] animalPrefabs;
 public int animalIndex;
 
 void Start()
 {
     
 }

 // Update is called once per frame
 void Update()
 {
     if (Input.GetKeyDown(KeyCode.S))
     {
         Instantiate(animalPrefabs[animalIndex], 
             new Vector3(0, 0, 20), 
             animalPrefabs[animalIndex].transform.rotation);
     }
 }

}