Mr. Su Bai and Lucy had a grudge because Mr. Su Bai, in order to clear his own suspicion, initially forced the role of the slandered upon Lucy. Moreover, from another perspective, Mr. Su Bai was Lucy's intended prey. Yet by a twist of fate, her attack on Mr. Su Bai actually assisted him in clearing his own suspicion. By the end, when the Housekeeper asked for votes, Mr. Su Bai sat there calmly, sipping tea while casting his vote under the pre-established control of the situation.
This was almost a form of humiliation, a mental humiliation of the likes of you lowlifes coming from a Senior Listener.
However, Mr. Su Bai didn't believe that the murderous intent in Lucy's eyes stemmed solely from their previous enmity. Lucy was not that simple, and neither were the audience naïve enough to kill purely out of hatred; otherwise, Lucy wouldn't have survived until now.
