Harry: You're sure about this, Neville?
Neville: Absolutely.
Harry: For an hour?
Neville: Most likely.
Harry: Most likely?
Neville: Well, there's some debate among herbologists about its effectiveness in fresh water as opposed to salt water...
Harry: You're telling me this now?

---

On their way to the lake, Neville slips Harry the Gillyweed.

---