Every phone shows four words: Lagos, Accra, Nairobi, Berlin. Most of the room sees it in under a second. Somebody overthinks it and gets it wrong. The board reorders.
The instant tappers bank 984 and 962. A second-guesser banks 612. A wrong tap banks nothing. Round two: saxophone, trumpet, drum, flute. Half the room taps drum. The other half decides drum is too obvious and taps flute.
By round five the room has worked out that some questions want the obvious answer and some want the clever one. The people winning have worked out which is which.