The prisoners tell Suigetsu Juugo is going to kill him, which makes him angry.
Sasuke and Juugo fight; Juugo is angry that Sasuke can copy his moves (he says like Kimimaro, which makes no sense to me)
Suigetsu comes in and starts fighting with Juugo.
Sasuke threatens to kill them both with a big snake if they don't stop.
Juugo turns normal, and is very scared.
Karin, having done nothing else, explains that Juugo doesn't actually want to kill anyone, and can't control himself when he goes into murderous rages.