Erevan was in a bad mood when he got back to Molly's house and turned into Casper. How could he have made such a huge mistake? Of course most humans knew how to kiss people properly!
He had spent months preparing to meet his mistress as a human man, went through all the trouble of setting up a real identity with proof of Evan Haimon's existence, and thought he knew everything about human courting rituals. All to realize that kissing required practice.
What was he supposed to practice on beforehand though? He didn't know any humans but Molly!
How could he have overlooked this? He even went as far as making sure he understood all the things she enjoyed reading or watching by doing it himself and looking up online discourse written by fans so he would know it inside and out. He guessed that was the best way to get her attention and had been right.