When Santana (Naya Rivera) accuses Finn (Cory Monteith) of outing her as a lesbian (after the Trebletones' "Rumour Has It/Someone Like You" performance) and slaps him, Finn's reaction to the slap is real. This is because the episode's director, Eric Stoltz, instructed Rivera to actually slap Monteith, so she did.
Mark Selling playing Noah "Puck" Puckerman at the age of 18 was in fact almost 30 during this episode.
In this episode they mention Jonas brothers and then in 2013 they broke up. And now they are back together in 2019. Up to now.