Next to optical humour may be placed acoustic--that of sound--another inferior kind. The ear gives less information than the eye. In music there is not so much conveyed to the mind as in painting, and although it may be lively, it cannot in itself be humorous. We cannot judge of the range of hearing by the vast store of information brought by words written or spoken, because these are conventional signs, and have no optical or acoustic connection with the thing signified. We can understand this when we listen to a foreign language. Hipponax seems to have been the first man who introduced acoustic humour by the abrupt variation in his metre. Exclamations and strange sounds were found very effective on the stage, and were now frequently introduced, especially emanating from slaves to amuse the audience. Aristophanes commences the knights with a howling duet between two slaves who have been flogged, "Oh, oh--Oh, oh--Oh, oh--Oh, oh--" In another play, there is a constant chorus of frogs croaking from the infernal marshes. "Brekekekex, coax, coax, brekekekex, coax, coax." In "The Birds," the songsters of the woods are frequently heard trilling their lays. As they were only befeathered men, this must have been a somewhat comic performance. The king of birds, transformed from Tereus, King of Thrace, twitters in the following style. "Epopopopopopopopopopoi! io! io! come, come, come, come, come. Tio, tio, tio, tio, tio, tio, tio! trioto, trioto, totobrix! Torotorotorotorolix! Ciccabau, ciccabau! Torotorotorotorotililix." Rapidity of utterance was also aimed at in some parts of the choruses, and sometimes very long words had to be pronounced without pause--such as green-grocery-market-woman, and garlic-bread-selling-hostesses. At the end of the Ecclesiazusae, there is a word of twenty-seven syllables--a receipt for a mixture--as multifarious in its contents as a Yorkshire pie.