Kanji is not sure he believes him and that is waaaaay too graphic a description for him just now. The reply that Jack's supportive and encouraging words are going to get is, "Uhhhhhh. Okay." What? It's a lot to take in for anybody much less him.
"I'll, uh, come back when you're all unpacked and stuff." As terrified as he sounds about that prospect he actually will. There's no way he can get like half the information he needs here and not follow up on it.