Sister-in-law had sex with brother-in-law

The brother-in-law was sitting when suddenly the sister-in-law came wearing a towel, the brother-in-law was nervous to see the sister-in-law in the towel, on the brother-in-law's asking, the sister-in-law said, I want to have sex with you, the brother-in-law did not understand anything, but then the sister-in-law also opened the towel.