"Subversion airlines thrives on the concept that “photocopying is cheap”. You are encouraged to make photocopies of your ticket, or to photocopy your photo ID, and give copies of each to as many people as you can. At checkin time at the gate, if more than one person arrives with a copy of the same ticket, they are ushered into the “merging room” and each person is given a brick. The door is closed, something magical occurs, and the one person that emerges still able to walk is allowed to board the plane"

If Version Control Systems were Airlines - The Changelog