How do i fix this? Health is not a valid member of Model... PLEASE HELP

Ok so here is the local script

 Player = game.Players.LocalPlayer
Mouse = Player:GetMouse()
Ammo = 1

Mouse.KeyDown:connect(function(key)
    key = key:lower()
    if key == "f" and Ammo >0 then
        local x = Instance.new("Part", workspace)
        x.Size = Vector3.new(20,0,0)
        x.Shape = "Ball"
        x.BrickColor = BrickColor.new ("Toothpaste")
        x.Material = "Neon"
        x.Transparency = 0.2
        x.TopSurface = "Smooth"
        x.BottomSurface = "Smooth"
        x.CanCollide = false
        x.CFrame = Player.Character.Torso.CFrame * CFrame.new(0,-1,-5)
        local v = Instance.new("BodyVelocity", x)
        v.velocity = Player.Character.Torso.CFrame.lookVector * 90

        v.maxForce = Vector3.new(math.huge, math.huge, math.huge)
        Ammo = Ammo -1
        wait(1)
        Ammo = 1







        local S = script["Script"]:clone()
        S.Parent = x
        x.Parent = workspace
        wait(2)

        x:remove()


    end

end)

But i made it so it can attack but gets that error heres the script that won't work.

script.Parent.Touched:connect(function(hit)
    if hit.Parent:FindFirstChild("Zombie")~=nil then
hit.Parent.Zombie.Health = hit.Parent.Zombie.Health - 4
         script.Parent.remove()

    end

end)

could someone tell me whats wrong and put the script down there thanks :D