Mistress Marta knows that she has a hot ass and a curvy one at that. So she was not looking for validation from anyone or even confirmation of how good her ass was. All she wanted was to dominate and humiliate the guy and she did it by farting on him as he stared and ogled her ass. That shocked him but she did not care whether he was shocked or not.
This guy wanted to punish her slave and she had to find a way to dominate the guy. The mistress wanted it to be something he would not forget in a hurry and that is why she chose to fart on him and choke him with her farts. The mistress had a great time dominating him and he learned his lesson the hard way and he never forgot what she did to him.
This guy was getting too comfortable with mistress Marta and she wanted to scare him a little. So she did what she does best and she dominated as well as humiliated him. He was shocked at how she made him a fart slave and asked him to smell her farts from her asshole. He did not have a choice as she had promised him some nastier punishments if he did not smell her farts.