Draco nodded and some tension seemed to drain out of him. "Good." He tapped the back of her hand with his wand, causing a very brief numbness that faded almost instantly; being able to short that part of the spell by touching the back of her hand was a good idea. "I've cast that spell on three people before today. One it terrified. One thought it was nowhere near controlling enough, which terrified me. And the third was me because I don't use spells on people that I can't stand being used on me." His tone turned wry and dark. "Of course I've had the Cruciatus from a range of experts."

He brightened up although it was visibly deliberate. "And what sort of safe word do you want? Of course most of the spells I want to cast on you are set up that a near-squib could cancel them with a wandless finite." He didn't mention that that spell in specific had a less pleasurable version that he'd hoped might hold Aunt Bella, and that wasn't designed to break.

Of course he hadn't released the spell on her; he wondered if she was going to or whether she'd leave it.