Why does the health change when i only change the walkspeed?

I'm trying to make a script that makes a player slow down when damaged. So, if my max health is 100 and my health is 50 and my speed is 16, my walkspeed should become 8. This is the code:

game.Players.PlayerAdded:Connect(function(player)
	player.CharacterAdded:Connect(function(character)
		repeat wait() until character.Humanoid
		local humanoid = character.Humanoid
		local originalSpeed = humanoid.WalkSpeed
		humanoid:GetPropertyChangedSignal("Health"):Connect(function()
			print("health changed")
			humanoid.WalkSpeed = humanoid.Health / humanoid.MaxHealth * originalSpeed
			print("walkspeed updated:", humanoid.WalkSpeed)
		end)
	end)
end)

It works perfectly fine, until this happens:

health changed walkspeed updated: 8 health changed walkspeed updated: 8.1613359451294 health changed walkspeed updated: 8.3214712142944 health changed walkspeed updated: 8.4838285446167 health changed walkspeed updated: 8.6445035934448

why does this happen, and how can i fix it?