"This little beauty's taught us more than all the teachers in this school."
-- Fred Weasley (PA10)
Incantation which opens the Marauders Map (PA10).
History and Notes
Both the Marauders Map and the incantations for using it were invented in the 1970s by the group of young wizards at Hogwarts known as The Marauders: Harry's father James Potter, his godfather Sirius Black, werewolf Remus Lupin, and future traitor Peter Pettigrew. The four also placed their nicknames in the map: Moony, Wormtail, Padfoot and Prongs (PA10).
References from the canon
- The Weasley Twins taught Harry the incantations to open and close the Marauder's Map so he could sneak out of the castle using the tunnels leading from Hogwarts to Hogsmeade (PA10).
- The Map would not open for Snape since he did not know the proper incantation, and indeed the creators had embedded insults meant just for him in case he ever tried (PA14). However, Snape was able to view the Map when Lupin left it lying open on his desk (PA19).
- When Harry suspected that Draco was doing something foul during 6th year, he told the Map "'I solemnly swear that I am up to no good ... or Malfoy is." However he couldn't catch Malfoy because he was inside the Room of Requirement, which did not show up on the Map (HBP18).
The Weasley Twins didn't explain to Harry how they learned to open and close the Map after stealing it from Filch's filing cabinet. When closed, the Map looked like a blank bit of parchment, and the Marauders certainly would not have left instructions. Knowing the way the Twins worked on their own projects it was possibly just trial and error that helped them discover the incantaion. It's also possible the Marauders had put enough of their younger selves into their Map so that it recognized a couple of kindred spirits who wanted to do mischief and break all the rules.
When asked about this, Rowling said:
JKR: Don't you — well. This is how I explained it to myself at the time, and this does sound glib. Don't you think it would be quite a Fred and Georgeish thing to say in jest, and then see this thing transform? Can't you just see them? Or, the map helped. And the map flickering into life here and there when they got closer and closer, and finally they hit upon the exact right word combination and it just erupts (TLC).