Carly teaches Kelsey about codes, Sherlock Holmes, and a serial killer who sucks at spelling.

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Sources:

Best Codes by zjawesome | instructables.com

Columnar Transposition Cipher | crypto.interactive-maths.com

Secret Codes for Cubs & Scouts | sites.google.com/site/codesforscouts/pigpen

One of the Few Remaining Ciphers Has Been Solved - Zodiac's Z-340 Cipher by Marcia Wendorf | interestingengineering.com