Before William can even speak, Silas interrupts him, "His white blood cells are being replaced by your...unique ones. He's displaying changes that make him look similar to you. After studying McCreary, I'm sure you won't look too similar, more like [dizygotic] twins."
Silas nods, smiling widely like a kid in a candy store. William looks a little more uncomfortable, rubbing at his head. "She...you're in here...too." He explains, awkwardly. "I'm just going to ignore them." He finally states, rubbing at his face with a gloved hand, "It seems easier than having to deal with listening to them."
"I'm sorry, Billy. It was the only way to save your lif--"
"Don't apologize. By the medic's accounts...I would be dead right now. I died several times, but eventually stabilized after...the transfusion. The thing I'm most concerned about...is how to tell my dad...that the Thornton line might die out."
You look confused, raising a brow. William looks embarrassed, glancing to Silas, who explains, gently, "Whatever this...process is, it makes you sterile." William winces and flushes, rubbing at the back of his head and rising to his feet with a clank of limbs.
"My prostheses aren't coming off anymore, either." He peels away a glove, to reveal the dark black metal beneath. "They put them on when I was first admitted to have better holds while moving me, and when I woke up I realized I couldn't remove them anymore." He walks over to the wall, pacing, for once, there's no smile on his face. "They're stronger, too. I don't think I'm stronger than you, though. Maybe more durable..." Finally, he snaps, "Oh shut up!"
He flushes again, glancing to you, "I always thought you were nuts. I see why."