Dan, Tim, and Mike are driving in Germany, and the GPS is in German. Mike changed the GPS language to German because he believes that it otherwise will not have the geographic information about Germany. As a result, they enter the highway the wrong way and anger other drivers.
Fred and George Weasley show Harry the Marauder's Map that they stole from Filch's office. The map shows all of Hogwarts and the movements of every person on the premises in real-time. The map also shows all of the secret passageways around Hogwarts.
Larry learns that Mrs. Tainot is playing music to drown out the GPS voice, which never stops. He then helps her turn off the "auto-on" feature on the very complicated GPS, which has no shortage of menus, submenus, and confirmation prompts.
After trying to devour the sub, the goblin shark realizes that it's not edible and spits them out, but breaks the Amphisub's GPS. Now the team on the Tortuga is on a mission to find the missing brothers.