Moving the character's torso without moving the entire character?

I'm making an idle animation and I'm trying just to have the torso move up and down without the whole character moving. Does anyone know how to do this?

cos = math.cos
pi = math.pi
t = char.HumanoidRootPart.RootJoint
c = CFrame.new
ca = CFrame.Angles


game:GetService("RunService").RenderStepped:connect(function()
    count = 0
    countspeed = 1
    count = (count % 100) + countspeed/10

    t.C0 = c(0,cos(count)/20,0) * ca(-pi/2,0,pi)
end)