How do I create a ray shooting downwards from my character's leg?

I'm trying to create a ray shooting downwards from my character's leg. I will later implement this into an NPC to prevent it from walking off the side of a cliff, but for now I'm just using my own character.

The problem is, I do not know how to get the ray to shoot straight down. I'm still pretty bad at vector math, but I thought if I were to take the leg's position and subtract 50 from the y, it should shoot down from the leg, because the leg's position just lost 50 studs of height. It didn't work. The ray did shoot downwards, but at an angle, not straight down.

The following code is in a LocalScript in StarterGui. No errors are in the output. The line you need to focus on is line 7.

local plr = game.Players.LocalPlayer
    repeat wait() until plr.Character
local chr = plr.Character

while true do
    wait(2)
    local ray = Ray.new(chr["Left Leg"].Position, chr["Left Leg"].Position - Vector3.new(0,50,0))
    local hit,position = workspace:FindPartOnRay(ray)
    print(hit)

    --Draw the ray for easy testing.
    local distance = (position - chr["Left Leg"].Position).magnitude
    local rayPart = Instance.new("Part", workspace)
    rayPart.Name = "RayPart"
    rayPart.BrickColor = BrickColor.new("Bright red")
    rayPart.Anchored = true
    rayPart.CanCollide = false
    rayPart.FormFactor = "Custom"
    rayPart.Size = Vector3.new(0.2, 0.2, distance)
    rayPart.CFrame = CFrame.new(position, chr["Left Leg"].Position) * CFrame.new(0, 0, -distance/2)
end