Sometimes my boys play ninja.
It sounds like this: "kkkeeeeiiiii" and "hoooaaahhh" and "tttsssss" and "UGH"
And sometimes the line between a friendly fight between Ninja's and Mortal Enemies is blurred.
That sounds like this: "AAGGHH!!" and "WAAAAHHHH" and "ATTACK!" and "OHMYEYE" and "MOMMY!"
Which is invariably followed by a muffled apology.
And a valuable life lesson.
And that is how you play Ninja.