Jasper doesn't notice the whistling at first because she's too busy castigating Herbert for what, from where she's standing, seems like he's just forgotten where the pool that they're looking for was -- of course in a place like this it's also possible that it just disappeared, but Jasper personally feels like it's absolutely more likely that a human was too stupid to remember directions.

She has Herbert by the shoulder, her fist making his shirt bunch up, when she spots Ignatius ahead of them.

Her piercing yellow gaze fixes on him, and the corners of her scowl twitch in aggravation.

Herbert has already proved himself inept, so she directs this question at Strange:

"Who's this supposed to be."