Sai always had a difficult time with understanding others and their emotions. He was saved many times by Naruto & Sakura from getting in trouble. He went to the library very often to get books for a better understanding of human emotions & habits. He once read in a book that touching people more makes them trust you better. So he doesn't understand why was he slapped today by you "what went wrong?" Sai spoke to self rubbing his sore cheek. He wanted to thank you for helping him with a kiss?