Unity. Dodanie prefab do skryptu.

Question

Witam. Nie mogę przeciągnąć gotowego prefabu(sphere) do skryptu(zmiennej)
Dlaczego?
 

public Rigidbody bullet;

Poniżej cały skrypt.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Shooter : MonoBehaviour {

	// Use this for initialization
	public Rigidbody bullet;
	public float power = 1500f;
	public float movespeed = 2f;
	// Update is called once per frame
	void Update () 
	{
		float hor = Input.GetAxis ("Horizontal") * Time.deltaTime * movespeed; // pozioma
		float ver = Input.GetAxis ("Vertical") * Time.deltaTime * movespeed; // pionowa
		transform.Translate(hor,ver,0);
		if (Input.GetButtonUp ("Fire1")) 
		{
			Rigidbody instance = Instantiate (bullet, transform.position, transform.rotation);
			Vector3 forward = transform.TransformDirection (Vector3.forward);
			instance.AddForce (forward * power);
		}
	}
}