Another Nick Story

The other day I was helping Nick on / off the potty, and he gave me an appraising look. "Mommy has hair on her nose?" he asked.
My sister Emily used to make comment like that all the time, especially when I was a teenager, informing me, in a loud voice that carried miles, that my eyebrows touched in the middle, or that my ears needed cleaning. So I'm used to innocent questions that actually have sting.
"Yes," I said. "Mommy does have hair in her nose."
Nick looked at me with an expression that told me he had a great idea. "Use Daddy's Nose Razor!"
I'm pretty sure he was referring to the electric shaver I gave Steve for Christmas six years ago, which had a nose hair trimmer attachment. Apparently I am not the only parent with hair on her nose.
I concentrated on not laughing, and Nick's expression got very thoughtful. He then, very slowly, put the tip of his finger up one nostril.
"I no have hair on my nose," he said, shaking his head. "Just boogers."

Why? Why do these things make me laugh?