Continuity mistake: When Walter tells Peter that the Cocabeans he bought can't be eaten, he takes the roasting pan off the bunsen burner. In the next shot, the pan is still on the burner. (00:06:55)
Continuity mistake: After Fauxlivia shoots Joe and is dragging him to the bathroom to dispose of the body, she hears a knock on the door. During this shot, she is dragging him with his jacket over his head, which she is gripping. However in the immediate next shot, she is still dragging him by his jacket, only the jacket is much lower.
Other mistake: Peter and Dunham are alone in an apartment with blood coming in under the door. They are called and leave for the subway. Peter should have had to walk through blood to leave.
Continuity mistake: When Walter is using the hammer on the block of ice, the pattern that results is different when viewed from each side.
6:02 AM EST - S3-E20
Continuity mistake: This is after Olivia has bumped into Walter in the hallway. She gets back into bed and tells Peter that his father is walking around the house naked. Peter laughs and says it's normal for a Tuesday. The sun is on Peter's left cheek in shots from behind Olivia. In the reverse shots from behind him, the sun is missing. (00:07:30)
Answer: He helped his father evade capture, impeding the investigation.