Incorrectly regarded as goofs: As ‘Planet Terror’ is an homage to the old, low budget Grindhouse films of the 70's and 80's, there are many deliberate errors by the filmmaker to give an authentic Grindhouse feel.
Revealing mistakes: (At 39:47) When Dr. William Block is about to inject Dakota Block with the yellow and red syringes, it is quite obvious that there are no needles in the syringes. At the point when Dr. William Block removes the protective cover off of the syringe with his teeth the missing needles is evident.
Revealing mistakes: In the jail cell scene where Wray (Freddy Rodriguez) asks J.T. (Jeff Fahey) if he's alright, he holds his gun upside down while he fakes handing it to the guard, he then shoots the guard. He is holding the gun by the frame. The gun is a 1911 style pistol. A 1911 style pistol can only be fired by squeezing the grip safety on the back of the pistols grip. The gun would never have fired in this case.
Continuity: In the hospital scene where Wray is searching for Cherry, he finds her by seeing her right boot next to her hospital bed. The infected tore off and took her right leg along the roadside, the leather boot was still on it.
Revealing mistakes: In the scene where J.T. is lying behind the counter in the Bone Shack assumed dead by Wray and Sheriff Hague, as J.T. awakes up you hear him cycle a pump action shot gun. J.T. is clearly holding a double barrel shotgun which has no cycling action. "Double Barrels" have a break open action where the barrels tilt forward for loading and unloading of 2 rounds only.
Continuity: At the end, when Cherry shoots the last infected in Mexico, the close-up shows she shot its head off down to the brain stem. But a split second later, when they show it fall to the ground, the head is (mostly) intact.
Incorrectly regarded as goofs: Cherry's gun-leg does not appear to have a function to fire and change ammo, but the leg was designed in the company of a bio-mechanical engineer that clearly has capabilities beyond a rational reality, so the fact that she doesn't need to pull triggers or activate different weapons in the gun-leg is rational, given the context and scope of the movie, along with the obvious fact that the technical functions of the device were deliberately overlooked by the filmmaker(s) to keep the action pace of the "grindhouse" film.