What does Graham say after do you...?

[svetlana14]

1. What does Graham say after do you...?


2. Do they use 's and 're correspondingly in he's my best mate and you're kidding? 0:44-0:47
https://youtu.be/1otHYspQUzU?t=44

 

[teechar]

A: "Did you know?"
B: "He was my best mate, growing up".
A: "You're kidding!".