What?

That just happens to be the most used word in our household.  If someone in the house is talking to you, your first reply must be, "what?"  It's an unwritten rule.

It doesn't matter if you are at the other end of the house or standing right next to the person talking to you, that is your reply. 

Coming in at a close second is "wait."  An example, "Wait, what?"  or "Wait, Mom.  Wait.  Wait.  What?"  Bella is pretty good with the wait-ing.  When you say something to her, lets say, "You need your library book for school."  The reply will be, "Wait, my library book?"  "Yes, your library book."  "Wait, wait.  I need my library book?"  "Yes, bring your library book."  "What?"

Tonight I was talking to Nick about something for school and he said, ..........."What?"  I replied, "what?" (I have to get in on it too, sometimes) and, of course he said, "what?"  This went on for a few minutes. 

The phone rang, an unknown cell number.  I answer the phone by saying, "hello."  From the other end I hear, "What?" 
Me:  I said, Hello.
Caller:  Wait.  I called by mistake.  (and hung up)

I told RT and he said, Oh, he must be from our family.  Why didn't you invite him over for dessert?