What is an inner demon?

"Besides, you might be able to find your mother in this way," Bai zixun continued after a pause.

Yun bixue's eyelashes fluttered as she looked at Bai zixun."Will I not have nightmares after going to my family's ancestral grounds?"

Bai zixun sighed."Yun bixue," he said."You have an inner demon."

Yun bixue's body froze, and her eyes widened. She looked deeply at Bai zixun.

Xie limo listened and held Yun bixue's hand tightly. It was as if holding her tightly like this would allow her to remain in his heart and by his side.

Yun bixue composed herself."What's an inner demon?" she asked.