It was an accident.

A man who binds himself with so many rules is afraid of what he will do without them. When all his righteousness is not enough and his little brother is killed by one he trusted, Nie Mingjue casts aside all restraint and principle. He travels to the Burial Mounds, his brother's corpse cradled in his arms, and kneels before the Yiling Patriarch, begging him to bring his brother back - And then he goes to seek an accounting. No matter what the cost.

“It’s not wrong if you write it down,” Mo Xuanyu muttered to himself like a mantra as he scribbled down a rough explanation of what he was going to do. “If you write it down, it’s just an experiment, and that makes it okay.” That’s what they used to say back at Koi Tower, back when they were doing all those bad things. They also said that you’re supposed to try stuff out before you do the real thing, because practice makes perfect. And anyway, surely it wouldn't hurt to put the cat in the middle of the body-sacrificing array before he put himself in - the array ran on resentment, on revenge, and how much resentment could a cat possibly have?