why isnt Thirst Script Not Working?

http://prntscr.com/ac4sy9 ** Script In Thirst Bar**

local Bar = script.Parent
local Thirst = script.Parent.Parent.Parent.Parent.Hunger


function Check()
	
	if Thirst.Value <= 100 then
		Bar.Size = UDim2.new(1.006, 0,1, 0)
	elseif Thirst.Value <= 80 then
		Bar.Size = UDim2.new(0.8, 0,1, 0)
	elseif Thirst.Value <= 60 then
		Bar.Size = UDim2.new(0.6, 0,1, 0)
	elseif Thirst.Value <= 40 then
		Bar.Size = UDim2.new(0.4, 0,1, 0)
	elseif Thirst.Value <= 20 then
		Bar.Size = UDim2.new(0.2, 0,1, 0)
	elseif Thirst.Value <= 10 then
		Bar.Size = UDim2.new(0.1, 0,1, 0)
	elseif Thirst.Value <= 5 then
		Bar.Size = UDim2.new(0.05, 0,1, 0)
	elseif Thirst.Value <=0 then
		Bar.Size = UDim2.new(0, 0,1, 0)
		script.Parent.Parent.Parent.Parent.Parent.Parent.Character.Humanoid.Health = 0
	end
	
end


while true do
wait(.1)
Check()

end

Get Thirstier Script

local Hunger = script.Parent.Parent.Thirst
local Amount = script.Parent.Parent.RateOfLoss
local Time = script.Parent.Parent.Time
while true do
wait(Time.Value)
Hunger.Value = Hunger.Value - Amount.Value
end 

UDim2.new requires four arguments. You only gave it three.

Simply put in a fourth argument and it should work;

gui.Size = UDim2.new(0.5, 0, 0.5, 0)

It works like this: UDim2.new(xScale, xOffset, yScale, yOffset)

To clarify if you didn't already know, GUIs use two different methods for size and position: scale and offset.

Scale is a percentage of your screen, while Offset is in pixels.

Scale will cause the GUI to be smaller the smaller your screen is, but if you use offset it will remain the same size on all screens.