He's trying to explain something important and complicated, and she sees something off in the distance that she's excited about. She grabs at his hand, but he's too busy using them in his explanation, so she gets a handful of his jacket instead and drags him along behind her, not paying any attention at all. He continues his discussion and doesn't notice for five whole minutes that she hasn't been listening. Love that they're in the shadow of the TARDIS too.
I absolutely loved when she dressed like that. Normally I couldn't care less about her clothes, but it really reminded me that, before the doctor, she wasn't this strong bad wolf, she was just a girl, trying to get through a days work