Well whenever isn't quite true - but more often than usual is definitively accurate!
In the past, Pixel would do her peek-a-boos when no one was immediately around and she wanted some attention and then she started doing it once her cage was covered, in the morning and then as well in the evening.
Now - in her cage with us around, covered or uncovered, anything goes.
And...she'll also say it if the Boy is in the birdroom with her and I'm not around until I show myself and she manages to get on me.
Maybe I'll get her to say other things as well in a more broad context - she has started to be particularly chatty, even outdoing her brother who used to be top chatty bird!