Great question, I don't why he does that other than show.
I have been working on tearing decks of cards. I can not tell you how hard it is. I know there are a lot of guys with really strong hands on here but it is hard and painful. The best I have done so far is a half a deck. It took me about a minute and I seriously thought my hands were going to come apart.
My wife got me 15 decks for Christmas so I have a fair amount to practice with.
What we think, or what we know, or what we believe, is in the end, of little consequence. The only thing of consequence is what we do. -John Ruskin