Eggshells are unusually strong and resilient structures that can be painted or used to hold other objects in crafts. Cutting an eggshell poses an interesting task as eggshells generally break apart totally after the surface has been cracked. If you use an object to score the surface of the eggshell (making small indentations to soften the surface), cutting the eggshell becomes an infinitely easier task. Don't expect to be able to cut eggshells perfectly right away -- with practice, though, you will have this down easy.
Use the marker to draw a line around the circumference of the egg, marking where you wish to cut it.
Take the triangular file and file away small chunks evenly along the marked line. Don't press down hard; simply file back and forth until a small indentation has appeared. Make about 10 indentations around the entire line.
Take the knife and press it into one of the indentations. Slowly work it back and forth until you puncture the egg. Draw the knife along the line, cracking the shell, through each indentation until you have completely cut around the egg.
Drain the yolk into the trashcan or a bowl for later use.