Continuity mistake: When Norma is eating at the diner with the college professor, she is eating a burger halfway through. Shortly afterwards the burger is completely new, intact. (00:19:53)
Refraction - S4-E5
Continuity mistake: When Chick delivers the window he uncovers it. When he leaves it is covered, then uncovered and recovered again.
Revealing mistake: At the beginning of the episode when Emma is talking with Norman, she drops the newspaper (of Bradley) in front of him. If you pause it and read the newspaper you can see the text has been repeated once for the text about Bradley and many more times for the news item below that. (00:41:35)
The Convergence of the Twain - S5-E2
Continuity mistake: After Norman dismisses Norma's suspicion about him going to "another business meeting" as childish, he heads for the door - the sunlight from outside is flagrant as he opens it. In the next scene, Norman is seen entering his car, in the same outfit, and it is night time. (00:28:15)