How can I fix this bug with humanoid.Health?

Ok so, I created this script for a sword game. It's basically a rehaul of that one classic Roblox sword. There's currently a bug where you can stack damage. Basically, if you have damaged the humanoid once, then use the sword 5 times, the moment the sword touches the model with the humanoid, it will deal 500 damage. The script is below.

game.ReplicatedStorage.SwordHit.OnServerInvoke = function(player)
    local character = player.Character
    if character then
    local hum = character:FindFirstChild("Humanoid")
    local anim = hum:LoadAnimation(script.Anim) 
    local arm = character:FindFirstChild("Right Arm")
    local humanoidRootPart = character:FindFirstChild("HumanoidRootPart")
    local sword = character:FindFirstChild("Sword") -- Sword is part of the StarterCharacter
    local strail = sword:FindFirstChild("SwordTrail")
        local dmg = false
        strail.Enabled = true
        anim:Play()
        sword.SwordSwing:Play()
        wait(0.35)
        strail.Enabled = false
        sword.Touched:Connect(function(hit)
            if hit.Parent:IsA("Model") then
                if dmg == true then return end
                dmg = true
                local hum = hit.Parent:FindFirstChild("Humanoid")
                if (hum ~= nil) then
                hum.Health = hum.Health - 100
                sword.SwordHit:Play()
                end
            end
        end)
    end
end

Any help would be appreciated, Thanks.