Grimy, broken and black

Several weeks ago, Nicholas checked out a book called Monstersong from the library. He loved this book, even though it's a disturbing tale about a mother pig who responds to her son's fear of monsters by pulling five of them from under his bed and tucking them in with him. Problem of monsters under the bed is solved, though not to the piglet's liking. He gets mom back in the end, but it still seems like an unnerving bedtime story to me.
Anyway, there's a line about Monster No. 2 that fascinated Nicholas:
"His nose was dripping and his nails were grimy, broken and black."
Every time I read this passage, Nicholas would stop the reading and ask about the monster's fingernails, why they were grimy and black. This would prompt a discussion of monsters' lack of proper hygiene and general indolence.
I returned the book to the library a few days ago, but the story wasn't finished.
This morning, I'm in the bathroom getting ready and I hear Nicholas coming up the stairs, giggling. When I go to look, he's covered in black marker: His nose, his hands, his arms, his legs, his feet. Even his toes is blackened. Every one. He's laughing and laughing.
"Look dad, my nose is dripping and my nails are grimy, broken and black! Look!"
How could I be angry about this?
Good thing it was washable marker. It still took a unscheduled trip to the bathtub to get it all off. Needless to say, I was a half-hour later than usual to work.