Little Z hears what she wants to hear. Example:
Z: Come up stairs and play with me! It's Turtle's birthday! We have to celebrate!
Z: Turtle isn't ready for a surprise. He doesn't know we're coming! So, just hide behind the blanket until I say when.
Me: But I don't want to go upstairs. And Turtle is just a stuffed animal.
Z: Okay, so when you're behind the curtain, I'll give the signal!
Me: I'm not going upstairs.
Z: You're hiding behind the blanket. Got it?
Little Z is now running up the stairs. Of course, I follow. It is, after all, Turtle's birthday, and we're going to surprise him. I am hiding behind the blanket until she says when.
It is clearly an advantage to adopt selective hearing earlier in life, rather than later.