I brought a 3”x5” block of wood when my high school chemistry teacher did this. He never actually described the other dimensions, after all. (It was a subtle protest from me because I had no trouble memorizing what I needed for that exam. I covered the block with unrelated physics equations.)

When I actually got to the exam he told us he wanted us to staple the card to the exam when we turned it in. The look on his face when I plopped the block of wood on his table, opened the stapler, and stapled the exam to it was priceless.