Carlsens cheap trick

Hi Guys.  
I would like to share some tricks from the game Carlsen - Aronian from Zurich Chess Challenge round 2. 

The game was very calm. But there were some interesting moments mentioned on press conference.
Here is the whole game. Take a look at it at first.  

ПОСТ НА РУССКОМ 

Why do you think Aronian didnt played 17... Nd7 ?
It seems so natural to bring the Knight to c5 and then to b3 .

"That's not a cheap thats a beautiful trick" - Carlsen said during press conference.
Why didnt black played 22... f5? Wasnt that the way to get an advantage? 

Thank you for your attention
Feel free to leave comments and share your opinion.

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