The phrase "curdle blood" typically refers to something that is deeply disturbing or frightening. Antonyms for this phrase would include words like calming, soothing, comforting, and peaceful. These words evoke feelings of tranquility and relaxation rather than fear or anxiety. Other antonyms might include words like cheerful, joyful, or happy, which suggest positivity and optimism rather than darkness and foreboding. Whatever the antonym used, it serves to counteract the intense emotional impact of the phrase "curdle blood" and to create a sense of balance and emotional well-being.