It takes a second for Peeta - who has already taken a couple of steps down the beach - to grasp what Daine is talking about. In his current state of mind, the mention of "people" makes him think of actual humans, and he immediately goes on alert, pivoting to scan the trees. Then Daine's meaning takes hold and he quickly steps back over to her, concerned.

"No. Daine - you can't help them." Knowing Daine as he does, Peeta understands that this will be hard for her, so he lays a steadying hand on her arm. "They aren't normal animals. They're muttations. You can't - they'll just hurt you."