To demonstrate, Pepperberg carried Alex on her arm to a tall wooden perch in the middle of the room. She then retrieved a green key and a small green cup from a basket on a shelf. She held up the two items to Alex’s eye.”What’s same?” she asked.
Without hesitation, Alex’s beak opened: “Co-lor.”
“What’s different?” Pepperberg asked.
“Shape,” Alex said.
National Geographic: Animal Mindsanimals birds intelligence