The couple who own Apollo (weirdly I don’t want to write “own” for such a smart animal, but anyway) are basically emulating the methods use with [Alex the Parrot] https://en.m.wikipedia.org/wiki/Alex_(parrot)

Apollo is impressive, but he’s not yet quite as impressive as Alex was.

For anyone interested in the subject of speech/language/higher communication in animals, a playlist of NativLang videos; Can Animals Grammar?