Revealing mistake: During his first transformation, the Hulk gets behind two soldiers and smiles twice. His second smile is too broad and reveals a very shiny silver tooth filling on his right lower jaw. David does have fillings but they do not cover the external area of the teeth (Ref: when he hugs Katie at the end of the 2nd part of Prometheus, right after his last transformation).
Revealing mistake: When the crew at Prometheus are viewing the tape of Hulk destroying the helicopter, it is obvious the tape is just stock footage from the scene earlier when the Hulk actually does destroy the helicopter. The camera angles used are exactly the same, and they are also angles the other crew wouldn't be able to film from.
Revealing mistake: When the Hulk is lifting his left foot at the beginning of his first transformation to break free from the "leg shackle", there is a close shot where we should see his toes. But we cannot see them because he is wearing some green pantyhose with brown soles to protect his feet.