When "Fauxlivia" receives the message instructing her where to go for extraction, the amount of the paper sticking up from the typewriter increases between when it stops typing and when she pulls it out to read it.
When Olivia is rescued from the operating table her face is marked showing where the cuts will be made. By the time she arrives at the Laboratory her face is spotless.
Walter strikes the key and listens to the sound, saying "E minor". E minor is a chord made up of three notes. - E, G, and B. The correct line should have been "E flat".
At around 3:55 the computers in the shot are running Windows 7. When Peter picks up a computer, the Apple logo on the top covers indicate they are Macs.
Peter examines the typewriter ribbon on the assumption that it works like a normal one. Were it normal, all the words would be on the same line, and not one line above the other.