How do I detect mouse movement with UserInputService?

I had assumed It would be a part of InputBegan like:

uis = game:GetService("UserInputService")
uis.InputBegan:connect(function(input)
    local inputType = input.UserInputType
    print("Input: ", inputType)
    if inputType == Enum.UserInputType.MouseMovement" then
        print("Mouse moved")
    end
end)

but UserInputType is never the MouseMovement Enum. Anything wrong here?