When Peter returns to Walter all the remaining bits of the books he previously sold, he enters the room wearing a 'slightly' rain-soaked, gray shirt.
After passing the box containing the items along to Walter, Peter sits down in a chair next to him and suddenly the shirt's soaked area is at least twice as big as before.
In the beginning Olivia asks one of the wedding guests if they can identify the unknown guy from wedding tapes and she says she absolutely can. They never follow through with this though.
In the Nazi's living area, an old gramophone is shown playing a regular 33 1/3 rpm record. But that disc will have been heavily scratched because of the weight and the size of the head and needle used on this 78 rpm gramophone player.
Walter very quickly examines the eyes of one of the bodies with a penlight and states there is "swelling of the vitreous humor." Visualizing the vitreous, which is in the back part of the eye, requires special equipment and cannot be done with just a penlight, and even with the proper equipment would take more than the couple seconds he spent looking. Furthermore, Peter confirmed the body he was looking at had it as well, and he didn't even have a light.
Walter claims the toxin could be programmed to target any group of people with a shared physical or genetic trait. Assuming he meant physical traits as a subset of genetic traits, and not that the virus is able to target non-genetic traits, he would be incorrect in saying it could be used to target a specific race. There is no gene sequence resolving to skin color or race, and, in fact, there is on average more genetic variance between people ascribed to a certain race than between the races.
In conversation with Walter, Peter states that 1933 (the year he erroneously believes his grandfather emigrated from Germany to the U.S.) was "well before the Nazis came to power". In fact, in January of 1933, Adolf Hitler, Nazi party chairman, was appointed Chancellor of Germany. This is generally agreed to mark the beginning of "Nazi Germany", and is exactly when the party came to power.