Seth's t-shirt changes color when he falls on the floor after being hit by Satanico Pandemonium.
When they are approaching the Mexican border, the same car pulls up twice and the same man gets out both times.
Seth Gecko's tattoos change between scenes. From when they are in the hotel, to when they are in the RV, there is a change in design. At first two parts of the tattoo are attached, in the RV, they are no longer attached.
Kate's t-shirt is still clean after lying on a floor covered with blood and other ooze.
At the motel when Richie is bending to pick up the keys after dropping them, Kate has polish on her toes, but a short while later in the RV when Rickie is staring at her she does not have polish on her toes.
The RV is heading into Mexico from the US and therefore would be subject to scrutiny and questioning by Mexican customs, not US customs as depicted. The only US border authority interaction would be payment of a crossing fee.
U.S Border Patrol Agents in Texas uniforms are green not blue, as shown in the film.
During the fight in the Titty Twister bar, Seth's 6-shooter fires more than six shots. This is a Robert Rodriguez director-trademark.
When Seth and Richie are in the Fuller's hotel room holding Scott and Jacob at gunpoint, Kate opens the door and stops when Richie and Seth point their guns at her, Richie then closes the door with her behind it but in the next shot of the door she is front of it.
At the bar, Seth offers Kate a drink but she declines saying she's not 21 years old yet. But in Canada and Mexico. The legal drinking age is 18. If Kate is 18-20, she could drink in Mexico legally.
However, it is possible that Kate doesn't know this, and believes that the legally drinking age is 21 in Mexico too.
When Seth Gecko gets knocked across the bar by Satanico Pandemonium, you could briefly see the mat that he lands on before cutting away to a close-up of him landing on the ground.
When Carlos shows up at the end, its presumably dawn, and he even remarks about how Seth wanted to meet in the morning. But based on the shadows, the sun is nearly straight overhead.
In the beginning with the robbery scene you can clearly see that Seth's gun is fake, when pressed against the head of Benny you can clearly see the orange tip.
During the fight in the Titty Twister, when the vampire's head rolls over towards Kate she actually misses the head when she tries to step on it. But in the next shot, it's sitting neatly under her foot.
Seth sets the clerk in the liquor store on fire. When the fire-engulfed clerk jumps up to shoot at the brothers again, you can see the fire-proof glove on his hand holding the gun.
Once Satanico Pandemonium ends her show, there is a close up
of Seth clapping his hands and saying "Now that's what I call a fucking show!" But in the next shot which is further away he is seen clapping his hands and mouthing the same thing again but no audio.
Lighting equipment, as well as the set's roof can be seen in several shots inside the bar after the vampire grabs Katie Fuller.
(at around 22 mins) You can see a camera slide into frame from the right.
The dolly tracks can be seen in front of the bar when the doorman talks about "wet pussies, dry pussies..." etc.
The border crossing in the film, from Texas to Mexico, is made over flat land. Anywhere you cross the border in Texas you must pass over the Rio Grande.
After they cross the border, Seth gives Jacob very simple instructions: drive straight forward until he meets a crossing road, then turn left. After they do they're driving towards a setting sun, however going south and turning left would have them face east, not west.
When Seth and the rest arrive at the Titty Twister, a local highway (presumably U.S.) can be seen in the background at twilight with several cars traveling on it.
When Seth and company are doing shots at their table, we can clearly see a background extra standing by the bar next to Razor Charlie playfully making hand gestures at the camera.
Jacob Fuller is established as a (lapsed) Baptist minister early on. When he is behind the bar in the weapon room, he blesses water and makes the sign of the cross. Genuflections and the concept of "holy water" are extremely Catholic.
After his hand has been shot, Richie can't use it. But while Seth is checking into the motel he is cleaning his glasses with the blown up hand.
The TV reporter refers to Seth as "the oldest of the two brothers." When comparing just two objects, she should say "the older of the two brothers."