This month I've been teaching a once-a-week class for nine- and ten-year-olds. At lunch on Saturday, three of them, two girls and boy, were sitting at the next table over. I walked over to check on them.
"How come you have those lines on your head?" the first girl asked me. "It's creepy."
"Well," I said, "either my helmet liner has seams, and the seams leave indentations where they press into my scalp, or a mad scientist snuck into my house last night and cut my skull open."
The second girl, clearly nobody's fool, said in an incredulous, the-question-is-its-own-answer tone, "Which is more likely?"
"I think it's the first one," said the first girl.
"I think it's the second one," said the boy.