The Rats in PackRat are computer-generated players that function independently and automatically within the game.
You can access the Rats' Packs (and other friends' Packs) by clicking on the magnifying glass at the top of the screen, which will bring you to the Explorer. Players can steal cards from the Rats, or flip the cards in their collection (by clicking on them) to win hidden credits, bonus cards, draw cards, retired cards, etc. Similarly, Rats can steal unprotected cards from your collection. Players cannot trade cards with the Rats.
Players can only flip Rats' cards a limited amount of times before needing to click a floating button to claim the credits won (this button appears in different parts of the screen and moves to prevent non-human bots from gaming the system).
Each user will see different cards when visiting the same Rat's pack, EXCEPT for Tom Ratterson, whose Pack does not shuffle, and whose contents every player sees.