Hagrid: Dumbledore sent me to parley with the giants. Hermione: Giants? Hagrid, Harry and Ron: Shhhh! Hermione: You found them? Hagrid: Well, they're not that hard to find, to be perfectly honest. They're so big, see?
When Dolores Umbridge leaves Harry Hermione and Ron come in. Hagrid tells them what he wouldn't tell Dolores Umbridge.