learning how to spell

This conversation took place in the bath today:

Me: How do you spell Zachary?
Zac: Z-A-C-H-A-R-Y!
Me: That's right! How do you spell mommy?
Zac: Mmmmmmm...M! M-O-C-H-A-R-Y! Yes!
Me: How do you spell Daddy?
Zac: Duh-duh-duh-duh....D! D spells daddy! D-A-C-H-A-R-Y!
Me: ok...How do you spell Tata.
Zac: T-A-T-A...C-H-A-R-Y!