Zombie Health Script Not working??

OK so i tried making a zombie health script also for it to get damage from a projectile (NOT RAYCAST) but even though it doesn't show any arrows for some reason when i try to shoot the zombie it doesn't work. Hers the script if anyone could halp me out thanks a lot!!!!

The Script:

 var health : int = 100;
 var bullet : GameObject;
 var damage : int;
  
 function Update () 
 {
     if(health < 0)
     {
        Die();    
     }
 }
  
 function OnTriggerEnter ( hit : Collider ) 
 {
     Debug.Log("trigger");
     if(hit.gameObject.tag == "zombie")
     {
        bullet = hit.gameObject;
        TakeDamage(); 
     }
     if(hit.gameObject.tag == "zombie")
     {
        bullet = hit.gameObject;
        TakeDamage(); 
     }
 }
  
 function TakeDamage()
 {
     health -= damage;
 }
  
 function Die()
 {
 
     Network.Destroy(gameObject);
  
 }