When Clem tells AJ the diamonds form in the "mantle of the rock" he actually meant the mantle of the Earth. Diamonds do not form in rock, technically speaking.
When eating cake while on the phone with Ruby, every time Louis takes another bite of his cake, he looks down at his plate. A blind person would never do this because they don't have spacial relation to things that is associated with sight, unlike the fully sighted actor playing the role.