Blind Rage - S3-E2
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).
Blind Rage - S3-E2
Revealing mistake: While pushing back the tank, the Hulk seems to be wearing light green loafers.
Answer: An illness, although it's never stated what kind of illness. David blames his dad for her death because his father never took her to the hospital. So in all likelihood, her illness was never diagnosed anyways and David might not even have known what it was.
Bishop73