NPC animations not playing?

i'm just trying to make 2 animations play with a while loop. They dont play, and theres no error message. Heres my script:

local hum = script.Parent:WaitForChild("Humanoid")
local anim = hum:LoadAnimation(script:WaitForChild("left"))
local anim2 = hum:LoadAnimation(script:WaitForChild("right"))

while true do
	anim:Play()
	wait(.18)
	anim2:Play()
	wait(.18)
end

any help?

There are two problems that I could think of, either the animation you're trying to play isn't yours, or your NPC is not the correct rig type to play the animation(r6,r15).