Bat has learnt how to say "no". Not just the concept (which she's been expressing very effectively for months already, believe me) but the word. I think we just managed our first proper conversation held all in words:
Me - Aren't you going to eat up your tasty crusts?
Bat - No!
Me - Oh, all right then. What would you like to eat now?
Bat - Marmer.
Me - A banana? [holds up banana]
Bat - Yeah yeah yeah!
It sounds like such a little thing but I'm actually quite excited.