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The way five metronomes synchronise over two empty drink cans, and the fact that the same principle explains how crickets sing in time ("A beat in time strikes a chord on YouTube", 15 May), is simply fascinating. I too have witnessed (with an amazing regularity) the same phenomenon in the street where I live: groups of young people start the evening shouting randomly at each other but, when they find themselves over a few empty cans, they start singing in time! However, contrarily to the metronomes, it normally takes them more than two empty cans to synchronise. Perhaps a matter of not-so-good vibrations.

Jos¨¦ Luiz Fiadeiro, Leicester.