However primates do not always fare so well in situations requiring theory of mind. In one experiment pairs of chimpanzees who had been close grooming partners were offered two levers. Pressing one lever would bring them food and another would bring their grooming partner food. Pressing the lever to clearly give their grooming partner much-wanted food would not take away from how much food they themselves got. For some reason, the chimps were unwilling to depress the lever that would give their long-time chums food. It is plausible but unlikely that the chimps figured there was finite food and it would eventually decrease their own food reward. The experiments are open to such interpretations making it hard to establish anything for certain.