Numbers has been though interrogations before. He was half expecting to get beaten by the police chief while Norman watched. He's all-too familiar with the language of direct violence, the kind the police are so eager to employ, and so he is caught a little off guard when Norman takes out the mouse. The only thing that betrays his curiosity is the slight quirk of an eyebrow.

His curiosity quickly morphs into horror when Norman injects the mouse with the first solution. Though he keeps face remains neutral and detached, he can't help but feel disturbed by the underlying threat. He'd fucked around before and been easily taken by the authorities to Norman's No-Good, Very Bad Dungeon. What was stopping him from doing this the next time he felt Numbers was acting up?

...But, then again, what had stopped him from doing it the first time Numbers fucked around and found out? He finds himself with more questions than answers. He watches, quietly, as the mouse is injected with the potassium chloride. The mouse is passed to him. He wraps his fingers around its still-warm corpse, staring down at it.

"I understand," Numbers replies, flatly.

Then, automatically, he turns to hold it out to Arthur.

"He injected a mouse with the bromide, then the potassium chloride," he mutters under his breath to him. "Open your hand. I'm putting a mouse in it."