Having the Bat around is like looking in a mirror sometimes. I didn't realise just how often I say "There!" when I've finished dealing with something - changing her nappy, wiping her nose, putting on her socks - until she started saying it too. Now I can't do anything without having it punctuated with a quiet little "Dere!"
Of course, it can be more embarrassing to have my behaviour reproduced in public - like the time she demonstrated to Batgran exactly how Mummy slouches down on the sofa and grabs the TV control. :-/