This exercise is for more than 4 players.
Two players choose a topic of conversation and the other players have to guess the topic. The two players talk about that topic without naming it and trying to lead the other players in the wrong direction.
If one of the remaining players thinks he/she knows what they are talking about he/she joins into the conversation. At one point he/she can whisper one of the players the name of the topic in his/her ears. If guessed right he/she can stay and keep on talking with the others, otherwise, he/she is out of the conversation.
The leaving player can join into the conversation again later. If he/she has not guessed right after 3 attempts then he/she is out of the game completely.
From the Book: Viola Spolin - Improvisation for the theater