The Question and Answer section for The Hunger Games is a great resource to ask questions, find answers, and discuss the novel.
I think this happens in Mockingjay, the third book. Buttercup is a mangy old cat which Prim loves. Katniss doesn't get along with Buttercup and thinks having a pet is the last thing they need to worry about,
Scrawny kitten, belly swollen with...
They sting the tributes if they are disturbed. They are very aggressive. Their poison instantly paralyzes the person and they convulse until they die.
When Katniss volunteers for Prim, the commentators are shocked:this is not a normal action. The commentators also do not know how to react when the crowd refuses to applaud: instead they give the silent salute.