Factual error: Two of the huge rocks which plummet from the roof of the cave hit the water and then bob to the surface again. Pumice is the only rock which floats on water, but this rock is white and pumice is grey, and pumice is too light and porous to form cave walls anyway.
Factual error: When Mouth flattens the tires on Brand's bike, all he does to let the air out is take the valve caps off. There's actually a valve in the valve stem that needs to be depressed to let the air out. The cap is just there to keep dirt out of the valve, simply taking it off wouldn't let the air out.
Factual error: As Stef is stepping down the fireplace, you can see that her Nike swooshes are drawn on her shoes. Nike never made shoes like that. Converse made them for a couple years in the 80s. (00:46:00)
Factual error: When the Fratellis break Jake out of jail, Francis shoots a trail of gasoline on the ground with his pistol, which lights it. In reality, this wouldn't happen, more than likely the bullet would bounce of the ground or embed itself, but not cause any sparks (if it caused any, wouldn't be long or hot enough to ignite) to light the gas.