Ivy likes hats. She will find one and hold it out towards us saying "Mmmm?", which means "make it work". When we put it on her head she walks up and down with a very proud grin patting the hat on her head. If she can't find a hat, then she will pat her head and look very concerned. And so 'hat' is the third sign she knows (after milk and eat, although eat can also mean drink or hot).
Ear defenders get a similar reaction.
"Mmmm?" can also mean "what is this?", although Ivy is now usually asking "Zis?". She is always very happy with the answer to that question. Lots of pointing is happening. Today I asked her "Where's Charlie?" and she pointed to him.