translation.en: You can teach them in the laboratory to do a little bit of exchange -- and indeed there's reciprocity in other animals -- But the exchange of one object for another never happens.
translation.zh: 我们可以教实验室的动物做一点点交换实验。 的确其他动物也有互惠关系。 但从一个物体到另一个物体的交换从没有发生过。