Why am I getting the "unable to cast value to object" error while trying to animate?

local toPlay = 4921133417 -- Animation ID

local anim = game.workspace.Dummy.Humanoid:LoadAnimation(toPlay)

anim.Looped = true
anim:Play()

I'm trying to make a dummy animated but I keep on getting the "unable to cast value to object" error, even though the "toPlay" argument is correct according to the wiki and object browser