The paper towels inside your body

Lucy (4yrs old) is having an ongoing, weeks-long (so far) discussion about what her body is made of. She starts with ticking things off on her fingers, “water, blood, bones, muscle, and” (she tilts her head for emphasis) “what else?” I mentioned organs and blood vessels and arteries and tissue, but, I said, “not the same tissue you use to wipe your nose.” She replied, “so where are the paper towels inside our bodies?” as she showed me a book full of diagrams of muscle and nervous and other systems.