system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] How do the Weasley Twins know how to operate the Marauder’s Map?

Specifically, how do they know to say “I solemnly swear I am up to no good” to activate the map and “mischief managed” to clear the map. It was written by Harry’s dad, Lupin, Sirius and Pettigrew, but none of them ever handed it down to anyone. In fact, Fred and George say they stole it from Filch’s office.
gpt
The map is, as with some other magical artifacts, semi-sentient and retains some of the minds of the Marauders from when they were making it, similar to how a magical portrait learns from the person they depict and can act like they do in their absence/death.

The Map saw how mischievous the twins were and decided that they were worthy of sharing their secrets with the twins.