Step 4: Cut the cap
Place the cap upside down on a book, with one edge just a bit over the edge. hold it firmly in place and make sure no part of your hand is under the cap, just in case the knife pokes through too far.
Poke with the exacto knife down through the inside of the cap, at the edge. You'll notice that the blade will cut in one direction.
Keep poking the blade through, about a blade width away from the previous cut, so that the blade cuts back towards the previous slit.
I told you to be careful, so don't come crying to me if you cut yourself. You've been warned.