"A farmer or young lad captures a leprechaun and forces him to reveal the location of his buried treasure. The leprechaun assures him that the treasure is buried in an open field beneath a particular ragwort plant. The farmer ties a red ribbon to the plant, first extracting promise from the leprechaun not to remove the ribbon. Releasing the leprechaun, he leaves to get a shovel. Upon his return he finds that every weed in the field has been tied with an identical red ribbon, thus making it impossible to find the treasure."
- from Dominic Tarr (private conversation)
A simple example of mix network:
"That had been a Slytherin System delivery, what you used if you wanted to communicate with someone without anyone else knowing that the two of you had talked. The sender gave an envelope to someone who had a reputation for being a reliable messenger, along with ten Knuts; that first person would take five Knuts and pass the envelope to another messenger along with the other five Knuts, and the second messenger would open up that envelope and find another envelope with a name written on it and deliver that envelope to that person. That way neither of the two people passing the message knew both the sender and the recipient, so no one else knew that those two parties had been in contact..."
- Eliezer Yudkowski, Harry Potter and Methods of Rationality