How to extrude the faces roundly? I follow the tutorial on youtube https://www.youtube.com/watch?v=-2uY7rjhhMs . 
At 7 min of the clip, he extruded the faces with rounded corners. Everytime I try, it doesn't look like that one. I think the way I did is pretty much right, maybe that guy using some kinda, trick or something like that. 
How can I extrude faces roundly like that guy?
I believe he has the subsurface modifier (Subdivision Surface) turned on (around 2:00).  He did not apply it so it's dynamic.