And, unrelated to the bird, there's a verb, "to quail." When you quail, you jump a little, or shake a little, or move backward, as if you're afraid. Here, Rosanna quails, dropping her snack, because she's suddenly afraid or surprised.
And even if you don't actually flinch or tremble or pull back, if you quail, that can also mean you lose your courage, as if you had been brave, but then you got too scared. This kiddo was pumped up and ready to go do something, but then he quailed and turned back.
What makes you quail? I would quail if I saw a snake. I quail at the thought of having to give a speech to a huge audience. And when I see my daughter take off running across a hot stretch of hard concrete, I quail at the thought of her falling down and hurting herself.
Usually it's people who quail. But your body can quail, and your voice can quail, meaning it shakes or trembles with fear. Even your heart or your spirit can quail, which can mean it shakes, it pulls back, or it stops being brave. My heart quails at the thought of jumping into an icy river.