When Claire gets the messages from the unknown 'friend', the alarm tone for the first message is different from the one for the next two.
Claire replies to an SMS from an unknown number. You can't do that because the phone does not have the number to reply to.
Angela looks at a newspaper article with the title "Civilain Deaths Reported in Angola Coup", an obvious misspelling of "civilian".
When Hiro and Ando jump off the pickup truck, in the wide shot the actor playing Ando is obviously not James Kyson.
When Nathan talks to Emile Danko the first time on the crater wall, his lip movement in the wide shot very obviously does not match what he's saying.