Continuity: When Sheldon is telling Leonard that he didn't ask Penny out, there is a yellow food-bag on the counter between them that keeps changing it's position with every shot change.

Continuity: When Sheldon, Howard and Raj play Jenga, there is one block sitting at the top of the tower. When Leonard walks in, there are now two blocks at the top, before we actually see Howard place the second one on the top.

Revealing: When everybody is on their laptops at the beginning of the episode, you can clearly see in many shots that their screens are black.