what are some instances we have seen so far that reveal the violent streak in Jack up to this point? (Chapter 1 and 2)

From the outset Jack is determined to put on a show of violence, "he snatched his knife out of the sheath and stabbed it into a tree trunk". Jack carries on in much the same fashion. When punishment for rule infringement comes up Jack says, "We'll have rules! Lots of rules! Then when anyone breaks 'em pow....." If Jack isn't being violent, he likes to exert the fear of violence especially on his choir in chapters 1 and 2.