Me: I have drawn a picture of a of the problem on the blackboard to show you what it looks like.
Them: So, what’s that white stuff in your hand?
Me: That’s chalk. Let’s look at the problem I have--
Them: Is the problem the chalk?
Me: No. The problem is what I have written on the board.
Them: There are lines on the board. This is problem because you rub this “chalk” on the board, producing the lines. Stop doing that and the problem goes away.
Me: It’s just a representation of the problem. An example.
Them: So... the chalk isn’t a real problem?
Me: No. What I have written in the chalk is the--
Them: Let’s try and see if the problem goes away if you don’t use this “chalk.”