6, actually.
And I love that moment!
Another good one is when Fred, George, Harry, and Ron are discussing the weapon in OotP, and Ron says something about how it must be huge, and Fred says; "Not necessarily."
"Yeah, size is no guarantee of power." (George) "Look at Ginny."
Harry asks him what he means, and George answers; "never been on the recieving end of one of her Bat-Bogey Hexes, have you?"