I've been in a riot. One moment, there's just a group of people gathering. It doesn't look threatening. Then you notice that their glances appear malevolent and there's a lot of whispering, or asides being said. Then comes the taunting. The crowd gathers. I saw it coming, and gathered my friends and said, "we're leaving, and we're leaving now!"
At first, they thought I was crazy. Later, I was asked how I knew. I said: "I used my effing eyes, and my brain!"