"I don't think she will," Strange responds, as he shifts Bell's position in his arms slightly. The hare looks over at Billie, blinking in a far too innocent 'look at me, I'm super cute and not murdery' sort of manner. "But wait until after we leave before shifting back to that other form of yours."

Because he did see that, right? That rat-thing was Billie. There's all sorts of questions that Strange wants to ask her (are you a shiftling? is this an enchantment? were you born like that?) but instead, he loosens his grip on Bell slightly and waits to see if Billie's going to mention anything about her other form.

He doubts she will. But he'll just be persistently nosy if that's the case.