"Peeta Mellark! Oh no, I think. Not him. Because I recognize this
name, although I have never spoken directly to it's owner. Peeta
Mellark. No, the odds are not in my favor today."
Page 25 (direct quote from book)
Katniss is shocked because she recognizes the name, and feels scared because Peeta saved her life before (by giving her the bread) and she is thinking how she will have to fight him in the Hunger Games.
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A kiss with peeta
Peeta fell in love with Katniss when they were young, and Katniss didn't return the feelings. Peeta was in love with Katniss before the story started, and Katniss began to like him back during the "cave scene" near the middle of the first novel.
In the first book, Katniss and Peeta both survive because Katniss pulls out poisonous berries (referred to as nightlock) and gives half of them to Peeta, telling him that if they both can't live, then niether of them should. In Catching Fire, Finnick, Beetee, Enobaria, Johanna, Katniss, and Peeta all survive because Katniss blew up the force field to the arena.
Katniss and Peeta's main connection is the bread. When they were little, Peeta had a huge crush on her, which was unknown to Katniss, and he took a beating from his mother and gave her a loaf of bread because she was poor and had no food.
She doesn't get to see Peeta because Peeta wants to kill her. Peeta was kidnapped by the Capitol and they used trackerjacker venom to corrupt the images of Katniss in Peeta's head so that when he sees her, he will try to kill her.