I read in a magazine the other day about a problem... You have a cup of tea. You start clicking with your tea-spoon on the cup and you put in som sugar. The sound of the clickings will change. Why? I guess that the sugar changes the density of tea, changing the speed of the soundwaves, chaniging the sound frequency which will ultimately change the sound of the clickings... Not a scientific explanation, but am I correct? Anyone have a better, more scientifc, answer?