Plankton?

Another typical conversation at lunch:
Hannah - That word sounded like what I'm learning, something like platonic.
Ray - You're learning about platonic?
Hannah - Umm, maybe it's plankton.
Mary - I know what plankton is.
Hannah - I do too, it's just something that floats in the water.
Sarah - So if I see a board floating by in the water, that's plankton?
Everyone else- No, that's just a plank!