Each phone shows four words: "Lagos, Accra, Nairobi, Berlin." Most of the room sees the answer in under a second. Someone is overthinking and gets it wrong. The leaderboard reorders.
The instant tappers bank 984 and 962. A second-guesser banks 612. A wrong tap banks zero. Round two: "Saxophone, trumpet, drum, flute." Half the room taps drum. The other half thinks drum is too obvious and taps flute.
By round five, the room has worked out that some questions are looking for the obvious answer and some are looking for the clever one. The good players have figured out the difference.