Character mistake: When Hank is brought to the hospital with gunshot wounds, the ambulance and its two EMTs are met outside by two doctors. One doctor says "Let's get him two grams of oxygen. What's his hemoglobin?" This episode's technical adviser was perhaps away for this scene. How much exactly is two grams of oxygen? Orders for administering oxygen would be given in liters, such as two liters per minute (LPM). The line is presumably meant to be 'two liters of oxygen'.
Revealing mistake: At the end of the episode when Tuco shows up at Walter's house in the backseat of Jesse's car, he tells Walter to get in. As they drive off, the shot pans out to show the street sign across from Walter's house. The sign says Piermont, which is the real name of the street. In the show, the Whites live on Negra Arroyo Lane.
Continuity mistake: In the scene where the shootout starts in the previous episode, Walter is handcuffed in the back of the SUV and trying to get to the floorboard to avoid the gunfire, and his glasses eventually fall off. After the gunfight when he is yelling at Jack from the back of the SUV, his glasses are back on his face, which would be hard to do handcuffed.
Continuity mistake: When Walt is sitting on the overpass it is clear that his car is parked on the part that straddles the median between the lanes, but when the shot is inside his car the view appears as if he is parked directly over the right lanes of traffic.
Character mistake: When Walt is in the bathroom using hydrogen peroxide to clean his leg wound he received from killing Crazy 8, he notices blood on his pants. He tries to clean the bloodstain off with a toothbrush. I think that any and EVERY chemist would know that hydrogen peroxide almost instantly removes blood stains from clothing. But, instead of using this somewhat common knowledge, Walt scrubs the stain with a toothbrush under the sink. Even if he had never heard of this 'trick', given the nature of H2O2 and Walt's understanding of chemistry, he would have realized this chemical solution immediately... Especially since he used the peroxide seconds before discovering the blood stain.
Factual error: Walter White correctly starts to lose his hair at the beginning of the chemotherapy. The errors occur afterwards (I know this from my own experience): 1. The mustache would fall out as well, 2. Walt has hair stubble throughout the treatment (and even has to shave his head!), while in reality a "chemo-head" is simply bald as a baby face since the hair is gone.
Continuity mistake: When Pinkman and White are having breakfast in the diner, the items on the table keep changing in each shot. Specifically, the jelly, the milk, the cup with the cream and, most noticeably, the rolled napkin with the cutlery inside: Sometimes folded, others opened.