To hard-boil the eggs, place them in a saucepan covered with water and bring to a boil. When the water comes to a boil, cover the saucepan and remove from heat for 12 minutes. Remove the eggs to an ice bath until cool, then peel and chop the hard-boiled eggs.
Mix the chopped hard-boiled eggs with the celery, raisins, yogurt, salt, and curry powder. The egg salad can be made ahead of time and refrigerated until ready to assemble the sandwiches. This will allow the flavors to develop.
Spread egg salad on top of 8 crustless pieces of bread and top each with another slice of bread. Carefully cut each sandwich diagonally in half with a bread knife. If the raisins are getting in the way of slicing through the sandwich smoothly, simply cut through the top piece of bread, move aside the raisins in the way of the knife, and continue cutting. It will be much neater than attempting to plow through the sticky raisins. Serve immediately.