They brought up the two babies without any discrepancy, in addition to conducting a comprehensive list of scientific experiments that included subjects such as "blood pressure, vocalization, locomotion, reactions to tickling, strength, manual dexterity, problem solving, fears, equilibrium, play behavior, climbing, memory, body size, scribbling, reflexes, depth perception obedience, grasping, language comprehension, attention span, and others,".
But eventually, Gua hit a cognitive wall: no amount of training or nurturing could overcome the fact that, genetically, she was a chimpanzee. "Our final concern is why the project ended like this.We are told only that the study was terminated on March 28, 1932, when Gua was returned to the Orange Park primate colony through a gradual rehabilitating process. But as for why, the Kelloggs, who are so specific on so many other points, leave the reader wondering".The experiment was meant to last for 5 years, following the growth of each child, but after just 9 months, Kellogg decided to ended it abruptly and mysteriously.It could be that the Kellogg was really drained from nine months of non-stop parenting and scientific work. Or perhaps it was the fact that Gua was becoming stronger and less manageable, and that Mrs. and Dr. Kellogg feared that she might be harmful for her human brother. However, one other probability comes to mind, the authors point out: while Gua showed no signs of learning human languages, her brother Donald had begun imitating chimp’s voices. "In short, the language retardation in Donald may have brought an end to the study”.