Percy pushed on his side furiously and the crack closed. His eyes blazed with anger. She hoped he wasn't mad at her, but if he was she couldn't blame him.If it keeps him going, she thought, then let him be angry.
Percy was intensely focused as he exerted himself to close a crack, displaying his anger through his fiery gaze. The tension in the moment suggested that he was channeling his frustration into action. Meanwhile, the observer felt a mix of concern and understanding, realizing that anger could serve as motivation for him.
Despite the possibility that Percy might be upset with her, she acknowledged that his anger was a natural reaction to the situation. She accepted that if his anger fueled his determination, it was a reasonable trade-off, allowing him to press forward in their endeavor.