Ron did, indeed, hear it and could think of no other response than a grim smile and a thumbs-up sign. He'd like to start hexing them rather than the Death Eaters at the moment for the way they treated Hermione when she was injured. His hands actually itched to do just that.
But then, he reasoned, if he did that, Hermione would most likely flay him alive. Instead, he merely shook his head and shot Harry another look that clearly said, 'Later.'