There is a very obvious continuity error which takes place when Barr is fighting the Bigfoot. Bigfoot bites off Barr's left ear and spits it out on the shrubs nearby. The bloody prosthetic ear is shown in a full close-up. Seconds later, when Barr pushes Bigfoot off of him, his left ear is shown completely intact with no facial injury, despite wearing a sling over the left side of his head afterward.
Shaving cream on Calvin's face changes positions during his beard removal in the tent.
When the cashier is speaking with Calvin about the lottery ticket, from behind, the cashier's face/head gestures do not match his speech.
In the beginning of the movie, the German in white uniform lifts the glass of alcohol to his mouth as the soldier in black approaches his desk. In the next shot the glass is on the desk.
Recently injured, still bandaged Calvin goes to dig up his grave to retrieve the wooden box. The grave site is flat, fully sodded, and undisturbed. It would have taken months for the grave site to look like that.
After Calvin foils the hoods' attempted robbery of him, he wraps one of the punk's gun in a handkerchief and breaks it on the road. It would not break in reality.
After a funeral attended by the community, where Barr is supposedly dead and buried, no one seems to notice when he moves back into his house and later attends a school play. These reactions are just not shown. (In a deleted scene, Ed points out that people aren't sure what to make of his return.)
Maxine (in voiceover) mentions watching the mailman put one of her letters through Calvin's door, but while we see her walk by his house, it clearly has a roadside mailbox out front.
When talking to Flag Pin on the phone, Barr says he shot Bigfoot in the head. Later, when we see Bigfoot's body, he's clearly been shot in the chest.
The "Dick Tracy" stamp called in the letter out was not issued until 1995.
When Calvin accepts the dinosaur from his little brother, he is wearing a US Army uniform in advance of his deployment to Europe. The patch on his right shoulder is that of the First Army, a large black A on a white and red field. This insignia was adopted 1950 - from 1922 to 1950 the patch was a large black A on a olive green field.
Vince Guaraldi's recording of "Cast Your Fate to the Wind" was on Fantasy Records. The turntable has a Columbia disc spinning.
The Canadian agent speaks with a Parisienne French accent. The French-Canadian accent is distinctly different from Parisienne French. To Canadians it's like having a character from the Bronx speaking with a Michael Caine British accent.
Both times when Calvin took off his shoe to remove the foreign object he puts his shoe back on without tying it up before walking away. He doesn't stop to tie it, but yet it is tied.