Even as she's looking at the stablehand rather than in Yondu's direction, Madoka immediately knows that his bad feeling was spot on the moment she hears that whistle. After all, Yondu showed her his arrow on his very first day on the train, back when they first met. She knows he controls it through whistling.

And there's no way he'd take it out like that over nothing.

So even though the stablemate just seems confused, Madoka knows there's no time to lose.

"Um, sir.. I-I'm sorry, but.. I think you need to see this.." Standing next to the stablehand, she activates the mana drive once more. Casting the same spell on him as she used on Yondu and herself.

And Madoka knows it works, because the man's eyes grow wide, even though he's staring at the same display as he was a few moments ago.

But it no longer looks the same to him.