Factual error: In his crude attempt to replicate the Human Centipede surgical procedure, Martin employs several handyman tools, including a carpenter's staple gun (using T50 staples as sutures). Problem is, carpenter's staples would never join soft human body tissues, they'd pull right out with little effort (T50 staples only join to very solid base materials, such as wood). Martin's victims, hysterical as they were, could have freed themselves from the T50 staples almost immediately.
Continuity mistake: At the end of the movie, the bloody handprint on the car changes entirely the second time it is shown. (02:02:45)
Other mistake: In the hospital, Barrett had his right arm in a sling and his lower left leg in a cast. When the police/ detectives were trying to find Barrett, one detective said Barrett could not have driven himself somewhere because he had "a cast on his leg." The cast was on the left leg, so Barrett could have driven using his right leg, as usual. Maybe he couldn't have driven with a cast on his right arm, but the detective gave the wrong location of the leg cast. (00:50:30 - 01:13:45)
Continuity mistake: Three teen boys are abducted to be killed at the church. One breaks free and finds a weapons cache and dies in that room, while his killer dies outside that room. Soon after, the preacher and his wife find the dead church member, then look into the weapons room to see two of the teen boys dead, side by side. But the second hasn't been killed yet, and dies running away from the church later, shot by the the local sheriff by mistake. (00:40:40 - 00:48:00)
Suggested correction: The second boy, the one who got shot outside, was playing dead so the church members would leave him. It is not a mistake in the movie.
Continuity mistake: In the 'match' when he tags with John Cena, Fred is picked up by the rival vampire in a fireman's carry position (kinda like for Cena's Attitude Adjustment), but his head is over the opponent's right shoulder in the first, wide, shot and towards the left shoulder in close-up.
Visible crew/equipment: As Max opens the bathroom door on the plane, a reflection of the crew is visible in the door. (00:50:10)