They tend to learn and repeat what ever appeals to them so each bird may select their own set of sounds. Our Greys all have words, sounds, whistles and song in their vocabularies. Each bird seems to have their own strengths and preferences. Pookie talks and sings mostly, Smokey Joe has the largest word collections but also whistles and makes some great sounds. Whisper my love bug her preference is sounds =wild birds Sparrows, Blue Jays, coffee pouring, pop tops and whistles but she does use a few words and Smarty Pants little Timneh is our whistle expert but also talks and makes human sounds-sneezes, coughs, clears throat and other less polite sounds. I think the more emotion is sounded in your words the more likely you may hear them repeat them.