This is already more physical contact than John has ever had from a person who isn't Arthur. Jack holds his hand very kindly, very warmly. After about five seconds John has no idea what he's meant to do with his other hand, or his expression, or any of his body language at all. He's beginning to look openly flustered when Jack lets him go.

This new revelation does not help him regain his footing.

"Your... best friend?" This strikes him as either a trap or a poor indication of character. His tone is politely cautious. "So he isn't... human."