Tom. She'd called him Tom. Again. And she'd said she loved him.
It had been quite some time since Voldemort had been driven into a state of rage that those few words managed to put him in. However, rather than roaring at her like some sort of uneducated buffoon, he coldly drew his wand.
"Silencio!" Aiming the silencing spell at his mother, he turned cold, heartless eyes upon her. "You will silence your tongue or I will remove it from your mouth." Staring at her for a moment longer, he turned back to Bellatrix if only to be able to calm himself before he killed the woman outright. He only lowered the spell after he'd looked away, although he was sorely tempted to keep it in place and simply toss her into the nearest room and forget about her existence.
"A change of clothing, Bellatrix," he stated. "Followed by a meal. Perhaps such common amenities will return Miss Gaunt's common sense and remind her of her proper place."