Step 1: 1.
write your letter or a secret message on a letter-sized sheet of paper
Step 2: 2.
and fold in half, lengthwise...
Step 3: 3.
and fold in half, again..
Step 4: 4.
Step 5: 5.
Fold together again, so that you have a thin strip of paper...
Step 6: 6.
and draw lines like this.
Step 7: 7.
and make a series of cuts alternately upwards and downwards. Let the cuts approach the edges but leave a piece of paper intact there.
Step 8: 8.
Step 9: 9.
Straighten the paper on a table. Make sure it doesn't get twisted. Unfold to get the original letter format. Straighten the folds with the side of your palm.
Step 10: 10.
Take the letter by the top and bottom and stretch. You will get a net and the message will be impossible to read. If you put the letter back to its original shape, you will get a readable message again.