While Wittgenstein is talking about whether the boundary between game and non-game is blurry, he picks up the topic of "seeing what is common". You know, this problem is famous in Plato/Socrates. This is the oldest arrow in Socrates' quiver: "No, tell me what all these things have in common". So this is real philosophy, though sometimes it doesn't feel like it to me. He talks about different ways of showing someone the color 'yellow ochre' or 'blue', and 'leaf'. He circles back around to wondering about what's in the mind of the user -- we've been here before in the Investigations, but now we have seemingly digressed from games back to this topic, but he's not really, he is applying these thoughts to the notion of game. He says:
"What does it mean to know what a game is? What does it mean, to know it and not be able to say it? Is this knowledge somehow equivalent to an unformulated definition? So that if it were formulated I should be able to recognize it as the expression of my knowledge? Isn't my knowledge, my concept of a game, completely expressed in the explanations that I should give?"(Wittgenstein, Section 75)
So here's an obvious question -- is the Philosophical Investigations itself a game? Is it a game he's defining during the course of the work itself, trying to avoid defining it so as not to privilege one of the standard games in the text itself? Is that why this is so difficult to get a handle on? Or should philosophy not be a game? If it's not a game then what is it? Should I have asked the last question? Oh dear, I smell self-reference.