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Write the note on a piece of paper small enough to fit inside the cap of a pen. Roll the paper and place it inside of the pen. Pass it to the receiver. After that, just wait for them to pass the pen back! They can replace your note with another note and pass it back. Just remember to watch the teacher! Take tiny post-it notes and stick them inside the textbook. Write different notes to direct the receiver like, turn to page 3, turn to page 66, until they find the note. It will look like you or the receiver is studying instead of reading the note.

Summary:
Ahead of time, get a friend to ask you to borrow a pen. Put your note in a certain page in a textbook.