Dr. Watson's "Migrating Wound"

A massive running joke in the Sherlockian community centers around Dr. Watson’s war injury. In the very first book, A Study in Scarlet, Conan Doyle writes that Watson was shot in the shoulder by a Jezail bullet. However, in the second book, The Sign of Four, Conan Doyle completely forgot what he wrote and stated that the bullet wound was in Watson's leg, causing him to walk with a limp. Fans lovingly joke that Watson was shot with a magical, migrating bullet that traveled through his body over the course of a year.