Continuity mistake: When Jennifer Walters is first introduced, her fingernails are unpolished. Later when she is restrained in Dr. Doom's lair, her fingernails alternate between being painted pink and red. Given that she and Bruce were running for their lives, she wouldn't have had time to paint her nails. Later when she transforms into She-Hulk, her fingernails turn green with the rest of her body, but if her fingernails were painted, they should still appear that color, as her skin and hair turning green wouldn't magically remove nail polish.
Helping Hands, Iron Fist - S1-E4
Factual error: When Bruce Banner sees the Hollywood sign reflected in the puddle of water, the reflection is backwards.
The Return of the Beast: Part 1 - S1-E1
Continuity mistake: When Banner is strapped to the chair and trying to resist transforming into the Hulk, the extent to how much he has transformed varies. Some shots will show his hands and head becoming larger, and the next shot will show him to instantly be back to normal proportions.
Darkness and Light: Part 3 - S1-E13
Continuity mistake: When Doc Samson tackles the new Rick Jones-Hulk hybrid and knocks over the cylinder for the nutrient bath, Banner spills out, and you can see he is wearing shoes. A few moments later when Banner begins to run outside, he is suddenly barefoot. (00:19:44 - 00:20:10)
Darkness and Light: Part 3 - S1-E13
Continuity mistake: When Ross is getting ready to sabotage the experiment, the equipment on the wall next to the fire extinguisher changes appearance. A white label also appears on the front of the extinguisher. (00:19:07)
Darkness and Light: Part 3 - S1-E13
Continuity mistake: When Banner re-engages Hulk in the desert after Hulk disposes of Talbot, the face guard for the exoskeleton armor Banner is using is missing, but then reappears when Banner launches the armor's right foot at the Hulk's backside. (00:07:38)
Darkness and Light: Part 3 - S1-E13
Continuity mistake: When Ross is threatening Banner with a gun, there is a shot that shows Banner frozen in place and the camera zooms out to show that the shot was reflected from the pupil of Ross' eye. Since it was a reflection, the flower on Banner's robe should have been on the viewer's left since the actual Banner has the flower on the viewer's right. (00:13:32)
Continuity mistake: When Gargoyle is standing in the doorway of the hospital room bidding farewell to Banner, they are standing at a straight angle respective to each other. When the shot changes, Banner has moved several feet to the left. (00:20:17)
Darkness and Light: Part 1 - S1-E11
Continuity mistake: When Doc Samson first breaks through the floor of the vehicle that is transporting the Hulk, his arm is emerging next to the platform that Hulk is secured to. When the shot changes, Samson's entire body is coming through the hole, and the base of the platform is nowhere to be seen. (00:19:54)
Darkness and Light: Part 1 - S1-E11
Continuity mistake: When Doc Samson is using the defibrillators on Banner, Banner's pants are suddenly adorned with a belt, which has disappeared when Betty starts cradling Banner's head. (00:15:20)
Darkness and Light: Part 1 - S1-E11
Continuity mistake: Just before Doc Samson tackles Talbot, Talbot fires his blaster, which hits the middle of a console. A couple of shots later, the blast mark is at the top of the console. Its size and shape change as well. In the wide shot it is nowhere to be seen. (00:14:00)
Continuity mistake: The cable Thor tears off from the suspension bridge to wrap around the Hulk changes from a copper color to silver. (00:06:25)
Darkness and Light: Part 1 - S1-E11
Other mistake: When Gabe Jones is observing Doc Samson and Hulk emerging from the cave system in his rear view mirror, you can see his car is moving forward, but the image in the mirror remains the same size. (00:11:10)
Continuity mistake: After Hulk breaks free of the cable Thor wrapped around him, he lands on the street and is hit by a car, which damages its bumper and windshield. When the shot changes the car is suddenly pristine until Thor lands on its hood. (00:06:35)
Darkness and Light: Part 1 - S1-E11
Continuity mistake: The nutrient bath container that separated Banner and Hulk was large enough for both to comfortably fit inside, but when Betty is trying to perform CPR on Banner, you can see an unconscious Hulk still in the container, and it is suddenly barely large enough for him alone to fit inside. The design of the container also changes. (00:14:20)
Darkness and Light: Part 1 - S1-E11
Continuity mistake: When Doc Samson kicks through the cab wall of the vehicle that is transporting the Hulk, he leaves a hole roughly the size of his leg, and the appearance of the damage suggests he kicked through metal. A couple of shots later, the hole is large enough for a person to fit through, and the appearance of the damage suggests it is now broken glass. (00:19:56)
Continuity mistake: When She-Hulk deflects the potted plant that Ogress throws at her, she gets dirt in her hair and on her arms and legs. When the shot changes, her hair and limbs are suddenly clean. (00:10:10 - 00:10:40)
Continuity mistake: Ogress is depicted as having five teeth. Two on top, and three on bottom. When she is saying to the Thing "Your chivalry is wasted on me," the bottom-middle tooth disappears. (00:08:50)
Darkness and Light: Part 1 - S1-E11
Continuity mistake: When Rick Jones comes to tell Betty that S.H.I.E.L.D. has taken the Hulk, he is standing by the door, and she is standing at the foot of Banner's bed. When the shot changes, they are both suddenly standing in front of a large window. (00:19:05)
Darkness and Light: Part 1 - S1-E11
Continuity mistake: When the S.H.I.E.L.D convoy is taking Hulk away, they are shown driving down a desert road, with large rocks on the shoulder. When the shot changes, the road is suddenly adorned with street lights. (00:19:43)
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.