Here and there it would happen.
The child would think it and then the thought would fly out of her backpack.
In any case, it happened enough to call it a “thought bag”, though it was nothing more a thick leather Coach backpack with a scuffed up vintage look.
And really, I think some thoughts are birds.
They hatch, flutter and fight to free themselves from their contained space, be it a bag or a head, then the thoughts fly away, and they are gone.