Metal Books

I shipped some stuff today, consisting mainly of computer crap and books.  I heaved the boxes on the post office counter and said the first and only first package was media mail and the rest were parcel post.  She marked the remaining boxes as media mail despite me clearly saying otherwise and after hearing the loud metal clunks on moving the box containing the projector and the box containing the computer case said “these are heavy, what are these books on?” My reply: “metallurgy”.