I just happen to notice. In the earlier chapters, when the main character transmigrates into the crown prince’s consort (when he plays "dumb"), he tells Qi Zhen that he smells of blood after killing someone. From then on, he repeatedly asks others if he carries that same scent, even though he only gave the order and never wielded the blade himself. He fears that the stench of blood clings to him and he'll (his majesty/emperor) smells it. 
Spoiler!
D I C K