Mommy Has A New Brain

Here's a hilarious discussion I had with my near 5 year old this morning in the car.

Son: "Hey, daddy, mommy has a new brain."
Me: "Oh, really? Where did she get it? Did she buy it at the store?"
Son: "Noooooh!"
Me: "That would be silly, wouldn't it?"
Son: "No, brains aren't silly."
Me: "Oh, okay. Well, what makes you think mommy has a new brain?"
Son: "Whenever she can't see me, she still knows what I do."
Me: "You mean like when you hit your brother, and she's not watching, but she still knows?"
Son: "Yeah."