Goofs

The amount and position of streamers on Raj changes between shots.

When Penny threatens to draw a smiley face in one of Sheldon's comic books, Sheldon refers to it as "blackmail", but it is actually extortion.

Howard claims that he had never had a threesome, but in the episode The Stag Convergence (2012) 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."

Correction: The threesome could have happened after this episode but before the later one.

When Howard fakes eating the peanut granola bar and Leonard goes to his bedroom to get his keys to take him to the hospital, Howard tosses the granola bar onto the coffee table as he calls Sheldon, then leaves it there as he and Leonard leave the apartment. Later in the ER, Howard pulls the granola bar out of his pocket to actually eat it to make his allergic reaction real.

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.