Continuity mistake: Sheldon is returning Amy's scarf and says, "You wore it the night we went ice skating, remember?" to which Amy replies, "You mean the night that I went ice skating and you stood at the rail Googling the symptoms of hypothermia." But in episode 8-12: The Space Probe Disintegration, Amy states that she cannot go ice skating because she has "unnaturally brittle ankles." (00:04:55)
Continuity mistake: In episode 16 of season 1, Penny is talking about making a cake for Leonard's birthday and states she knows his birthday because she was checking a horoscope for him. But in this episode she does not know when his birthday is, which leads to Leonard revealing he was secretly reading Penny's diary. (00:40:00)
Continuity mistake: In the first half of the episode while in Las Vegas, Penny's hair is short; however, later in the episode when she is back in the apartment speaking with Sheldon, her hair is much longer, albeit tied back in a bun, but very obviously much longer and a very different color. The scene from Las Vegas to her apartment was less than 24 hours apart and would have been impossible for her hair to have grown so much.