The amount and position of streamers on Raj changes between shots.
Howard claims that he had never had a threesome, but in the episode "The Stag Convergence" Raj drinks a toast to Howard at his stag party and tells the group of their encounter with a woman dressed as Sailor Moon at Comic-Con: "The only threesome I've ever had in my life, and I'm proud to say it was with this man right here."
When Penny goes across the hall to propose holding a surprise party for Leonard, she knocks on the door and waits for Sheldon to answer it. In previous episodes she knocks on the door and just walks in.