(My sister and I were left home alone.)

As I am doing my business in the bathroom, I hear knocking at the door. I assumed it was my sister and asked

"Hey xxx, are you knocking at the door?!"

No response.

My phone rings and I answer only to be met by my sister's voice.

"Hey, I'm at the store, what do you want for dinner?"

I hear her through the phone, but I don't hear her through the door as the knocking continues...