I would like so much my cockatiel to say "Mum" (or "Mom"

) to me.... Maybe he already does, I repeated the word to him several times, but it is such a short word, and cockatiels don't speak clearly, so he might already be calling me mum...
Yesterday I noticed something really funny. He was very nervous, climbing up and down the cage, pulling the tail of his toy mouse.... I started playing and he closed his eyes
immediately, LOL. But I noticed that his crest was still up, which actually means he is paying attention, so I wonder if he just closes his eyes and daydreams, but is not actually sleeping.... That crest is somewhat suspicious....

Also, usually when he goes to sleep he puts his head under his wing...