Applying Collision Groups to Player?

I'm trying to make an unanchored brick, stored in ServerStorage, uncollidable with the player. If I turn CanCollide in the brick off, it'll just fall through the ground, so I need to use collision groups. The script I have right now doesn't seem to work, and I'm not sure why.

local PhysicsService = game:GetService("PhysicsService")

local bell = "Bell"
local characters = "Characters"

PhysicsService:CreateCollisionGroup(bell)
PhysicsService:CreateCollisionGroup(characters)

PhysicsService:SetPartCollisionGroup(game.ReplicatedStorage.LooseBell, bell)
PhysicsService:CollisionGroupSetCollidable(bell, characters, false)
PhysicsService:CollisionGroupSetCollidable(characters, bell, false)


local function onCharacterAdded(character)
    PhysicsService:SetPartCollisionGroup(character.Torso, characters)
    PhysicsService:SetPartCollisionGroup(character.Head, characters)

end

function playerAdded(plr)
    plr.CharacterAdded:Connect(onCharacterAdded)
end

game.Players.PlayerAdded:connect(playerAdded)