... the Naos also had to recognize the referee's whistle themselves. Team 'B-Human' used a recognition system that had been trained to make exactly one whistle sound so that the robots in the hall full of soccer pitches would not react to the whistle from the neighboring competitions. So much for the theory. However, practice showed that the whistles used in the game did not always produce the same sound and so recognition did not always work. Other teams used more tolerant approaches, which meant that recognition worked better there. However, as expected, these robots sometimes heard one or two whistles too many. For the 'B-Human' team, ...