Continuity mistake: When Stewie is building with blocks, you first see a pyramid with three blocks on the bottom and two on the top. The shot changes, and he puts two more on the top, near the edge. When the shot changes again, suddenly there are five blocks on the bottom, six on the second layer, and two on the top near the middle. The letters and pictures are also all different.
Continuity mistake: When Stewie is in his room talking to Rupert and himself out loud about Janet we see that Rupert is on the left side of Stewie's pillow. When the camera pans over to Brian who overhears Stewie's musings, after Brian makes fun of Stewie the camera pans back and Rupert is gone. There is also a quick tete-a-tete on the color of Janet's eyes and the final shot is on Stewie and his crib and yet no Rupert to be found.