attempt to index a nil value problem?

im having this problem :attempt to index a nil value i want to fix it there is the script:

function onTouch(part)

local human = part.Parent:findFirstChild("Humanoid")

if human ~= nil then

part.Parent:findFirstChild("Head").Transparency = 0.98

part.Parent:findFirstChild("Torso").Transparency = 1

part.Parent:findFirstChild("Left Arm").Transparency = 1

part.Parent:findFirstChild("Right Arm").Transparency = 1

part.Parent:findFirstChild("Left Leg").CanCollide = true

part.Parent:findFirstChild("Left Leg").Transparency = 1

part.Parent:findFirstChild("Right Leg").CanCollide = true

part.Parent:findFirstChild("Right Leg").Transparency = 1

end

end

script.Parent.Touched:connect(onTouch)

--COLORS

--1 = white

--208 = Light stone grey

--194 = Medium stone grey

--199 = Dark stone grey

--26 = Black

--21 = Bright red

--24 = Bright yellow

--226 = Cool yellow

--23 = Bright blue

--107 = Bright bluish green

--102 = Medium blue

--11 = Pastel blue

--45 = Light blue

--135 = Sand blue

--106 = Bright orange

--105 = Br. yellowish orange

--141 = Earth green

--28 = Dark green

--37 = Bright green

--119 = Br. yellowish green

--29 = Medium green

--151 = Sand green

--38 = Dark orange

--192 = Reddish brown

--104 = Bright violet

--9 = Light reddish violet

--101 = Medium red

--5 = Brick Yellow

--153 = Sand red

--217 = Brown

--18 = Nougat

--125 = Light orange