Chapter 20: What does Katniss do to ensure that Peeta won't follow her to the feast?

They eat the soup as Katniss plots how she can get him asleep long enough to escape, knowing he is serious enough to potentially try and follow her. She comes on no solution until, while gathering water at the stream, a silver parachute comes down. It's not infection medicine, but sleep syrup, which she takes as a rather cruel choice on Haymitch's part. But the message is clear enough, and so she mixes the syrup with some berries and uses the concoction to knock Peeta out.