How can I discipline this?

Sofia waits until I go into the bathroom and then she strikes! Yesterday night while I was busy she went into the fridge. This is our conversation that took place after:

M: Sofia you aren't allowed to go into the fridge by yourself.

S: (hides her eyes and runs passed me into the living room)

M: Sofia this is no joke...

S: a goat?

M: No goat Sofia, not a joke. You can't go into the fridge by yourself. Do you understand me?

S: baaaaaa

I kid you not! I'm in big trouble. She said this with THE most impish grin on her face. She knew that she was in trouble and the was trying hard to "cute" her way out of it. I'm still laughing over it. The funniest thing is that this is how Grant gets out of trouble too, he can always make me laugh.

Oh well, I may not have the best disciplined kids on the block but at least our house will always be filled with laughter!