Where does this come from?

The other day Ray asked me if the speck of dust he found was a molecule.

We also had a conversation about coals. It went something like this.

Mommy, what are hot coals? (Coals are what is left when a fire goes out. We also use coals to burn in our BBQ).

Do coals glow? (Yes, when they are hot).

But when you pour water on the fire, it goes out and the coals are not hot anymore. (That's right)

What are coals made of? (Well, that depends on what you use to make your fire. I think coals are mostly made of carbon.)

Oh, that's right Mommy. Are coals dirty? (Yes, usually.)

Are coals greasy? (No, I don't think so.)

Bicycles are greasy. (........)