"Nakum Peaz"

In the car this morning-

Emerson: I need a nakum peaz mommy
Me: To wipe your nose?
Emerson: Yes
Me: Okay, but please do not rip the napkin up into little pieces. Hand it to mommy when you are done.
Emerson: Ok Mommy
Long pause
I turned to check on her and all was well with the napkin.
Me: Emerson are you finished wiping your nose?
Emerson: Nope
Me: Hand it to me when you are finished.
I Called Denny on the phone and had a 2 minute conversation. I hear her tearing the napkin apart. Look back and she has torn the whole thing up.
Me: EMERSON. Did you tear the napkin up?
Emerson: Yes
Me: Did mommy ask you not to do that?
Emerson: Yes
Me: You are in trouble. Why did you do that?
Emerson: I not know why I dood that.

What could I say to that?