It's the noise she makes when she swallows. She wants to nurse, and she invented her own special series of words for it. I'm fairly sure she's actually capable of saying the word, "nurse" or at least, "drink" but every time I ask her to she shakes her curly head and says no.
Nyuk, nyuk, nyuk,
I will not give in to this. I'm going to keep calling it nursing. I'm going to win this one.