Other mistake: When the elder Tongzing and Tenzing walk through the bushes, they simply pass through them, the bushes don't react to them moving through. (00:18:50)
Other mistake: When we see Betty being surrounded by the ninjas reflected in the pupil of Bruce's eye, the reflection is not reversed. (00:02:08)
Answer: The Hulk is a giant brute who smashes everything in his path when he is angry. In Ang Lee's "Hulk," General Ross, played by Sam Elliot, explains it to his daughter.