While Conway also names FarmVille, Mafia Wars, and CityVille in his lecture on Facebook games, he uses Pet Society's social features to build his strongest case. We've all known about the "Cafe" in Pet Society, a location in the game where everyone can go to show off their pets and their pets' homes.
Charles Conway Pet Society BunnyPig
Pet Society Go to ProfileBy being in the Cafe, you're bound to meeting strangers. Even though all you can do once you get to another pet's home is some pre-set actions (e.g. hug, kiss, dance, laugh, and punch), there's also the option to visit the real Facebook profile of a someone you might not know at all. Conway actually demonstrated this by creating an avatar named "BunnyPig" to demonstrate to a group of foster care and social workers.
Because Facebook games require players to have lots of friends to earn virtual money and goods, Conway concludes that kids will be tempted to friend strangers. And in turn, malevolent strangers can scope out kids who play the game. This "Go to profile" option is clearly a valid concern and does exist in the game.