When Shawn and Gus first see Jonny G. slumped in the car, Jonny's head is tilted forward over the steering wheel. But when they move closer to investigate, Jonny's head is tilted backward over the seat.
When Lassiter is driving the Blueberry the headrests are missing, but when Shawn and Gus pick it up at the customs shop they are back.
When Shawn and Chelsea kiss, their heads are alternately tilted to the right/left between shots.
Nitrous oxide gas for custom cars is blended with sulfur dioxide gas, which causes severe nausea and vomiting, in order to prevent recreational huffing. When Shawn and Gus are exposed to the opened NOS tank in Johnny G's car, both should have become violently ill rather than simply giddy.
When Buzz Mcnab pulls over Shawn and Gus (shortly after Shawn gets Gus' car pimped out) you can clearly see Mcnab's lips staying still while his lines continue to play out.
Shawn and Gus joke that a "female Mustang" is an oxymoron. However, a Mustang is a breed of horse; the term does not refer to the animal's gender.
Juliet reads the vest manufacturer's advertisement that claims the vest can stop a "tank mortar shell". A tank's weapon is called a "main gun" not a mortar, and is a direct fire weapon. A mortar is a very different type of weapon that works by indirect fire similar to artillery. This is as different as a rifle is to a shotgun.