“I solemnly swear that I am up to no good.”
These are the words required to reveal the Marauder’s Map. Of course Fred & George Weasley were able to come up with these magic words - they were always up to no good. They passed the words along with the map to Harry so he could get to Hogsmeade in his third year, but the map ended up being used for so much more!
Enjoy this compilation of Fred and George moments from the movies: