Summarize this article in one sentence.
You can trick a person into jinx by asking a simple question. For instance, if you say "What's 2 plus 2?," the other person will mostly likely say "4." In that case, you can say "4" at the same time, then immediately say "jinx" to start the game. In some variations, the person doing the jinxing can punch the jinxed person if he or she talks before the game is over. In one variation, when you say the same phrase, you can say "American jinx, touch wood" instead of just "jinx." You play the game the same way with one exception: the first person to touch a piece of wood gets to punch the other person. If you both say "jinx" at the same time, you can say "double jinx" to initiate the game. In that case, you need to say the person's full name to end the game. If it happens again when you say "double jinx," it turns into "padlock jinx," where you need to include the person's middle names to end the game.

Summary:
Trick a person into jinx. Know a variation. Understand the "American jinx" variation. Try double jinx.