A philosophical conundrum I saw posted on a shop window in Tokyo: [Crinkles brow and scratches beard] The vending machine sells the drink, but does not the drink also sell the vending machine? Surely, without the drink the vending machine would be nothing; indeed, it would be entirely redundant in its purpose. Therefore one could propose that the drink, being demanded by many, is in fact the sole factor behind the selling of the vending machine. In other words, "The drink also sells the vending machine". [Leans back in armchair and takes a victorious puff on his pipe, whilst tugging down woollen cardigan in air of triumph]