When a fire ball launches itself at Katniss, why does she retch twice?

she threw up twice because she's nervous.

She was sucking in all the acid from the fire attack. That's when she retches twice.

She was sucking in all that smoke in the air and then she takes cover to retch twice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What did you think she was doing huh?

She was sucking in all the acid and smoke from the fireball attack. So she throws up twice to get rid of it. She loses her meager supper and whatever else she had. [Supper, water etc].