As far back as Charles Darwin, scientists have noted that apes make characteristic sounds during play or while being tickled, apparently to signal that theyre interested in playing.

• 早在查尔斯?达尔文时期，科学家就已经注意到，在玩耍或者被瘙痒后，猿类会发出特别的笑声，这似乎表明它们很喜欢玩耍。