Apparently this was to be a force of wills then. But Bellatrix was confident that she would win. She was stronger than both of these children and she would break the both of them before the night was over. She saw what Remus was doing, how it was working and she dug her fingers further into Remus's wound, stretching and tearing at the already tormented flesh in an attempt to distract him.
"He doesn't love you," she sneered. "He tore you from your family. He only loves you when you reject who you are." She gave another push of her mind into Sirius's, long past the point of not wanting to overly influence her cousin. No, now she just wanted to finish this. She wanted Sirius to do his worst to Remus, to go past the point of forgiveness. You know he is lying. He will say anything to get you to stop inflicting the punishment that is due to him, for all he has done. Pick up the knife and drive it straight through his foot. Through his foot and into the ground. Make him pay for trying to manipulate your feelings like this.