ShuiEro ... from vague up to sometimes ;) crystal clear drop by drop ...

Four psittacids—an African Grey parrot, an Illiger macaw, a cockatiel, and a parakeet—were tested on object-permanence tasks that are commonly used to assess levels of understanding in human infants during their first 2 years. These birds showed Stage 6 competence, demonstrating that object permanence is not limited to mammals. The results for these birds were comparable to those of an African Grey parrot that had been trained in interspecies communication prior to object-permanence testing. Our findings thus suggest that although language-like behavior provides a communication channel that facilitates testing, such language training is unlikely to affect the outcome of the tests.