A Membership Game
Bobby's World is an example of a secret rule game.
A secret rule game is a playful, often puzzling group activity where one or a few players know a secret rule that determines what fits or happens in the game, while the rest of the players must figure it out through observation and deduction. The fun lies in the mix of confusion, clever hints, and the "aha!" moment when players crack the code, making these games perfect for sparking laughter and creative thinking in social settings.
Like all secret rule games, Bobby's World is played in a group where some, but not all, players know the secret rule.
Bobby's World is also an example of a Membership game.
In a Membership game, gameplay revolves around organizing things into groups based on a specific quality. Anything that can be discussed — a person, place, thing, or otherwise — may or may not have that quality. Players who know the secret rule understand the criteria that determine whether something is legal in Bobby's World.
Gameplay in Bobby's World revolves around players gathering examples of something that either is legal in Bobby's World, or not.
There are two ways examples can be provided. First, a player who knows the secret rule can volunteer an example, identifying whether it is legal in Bobby's World. When providing examples, it is often helpful to offer two things that are similar in some respects, but only one of which is legal in Bobby's World — the contrast gives the other players something to reason about.
Second, players who don't yet know the rule can suggest something new and ask the knowers whether it is legal in Bobby's World. Knowers respond at the same time, building up a body of examples for the unknowers to deduce from. While questions will almost always be answered with "yes" or "no", there are some cases where the answer may be less concrete, which can give players further clues about the secret rule.
The game ends when all players have figured out the rule and can agree on whether something is legal in Bobby's World reliably. Those players will no longer be able to play that particular game, but there are plenty of other secret rule games to try next.
Reveal the secret to Bobby's World
A thing is legal in Bobby's World if and only if its name is spelled with double letters.
One thing to consider when playing Bobby's World is whether all the words in a phrase or description have to have double letters for that thing to pass through, or whether any word in the phrase having double letters is good enough. For example:
Is Cookie Monster allowed in Bobby's World, even though a Monster isn't?
My recommendation is to only require one word in the phrase to have double letters. There are other games that share the rule where requiring every word to have double letters makes more sense.