Snoopy makes only two pizzas, but when he returns to the oven there are four visible. When he stacks them, there are five, then when he brings them to the table, there are six, but when Charlie Brown decides something is wrong with him, there are five again.
When Snoopy goes to sleep on his snow doghouse in his nightmare, the wire to his harness is in back of the doghouse, but when in the morning before he wakes up, the wire is in front of the doghouse.
After Charlie Brown says "Oh brother". Snoopy's pizzas change animation design and 2 more drinks appear next to the milkshake which changed positions.
Some of Charlie Brown's claims and some of the events that occur during Snoopy's nightmare are inaccurate. For example, most Siberian Huskies, Malamutes, and other sled dog breeds are not fed once a day, nor do their meals mostly consist of cold meat and raw fish. In real life, they eat regular dog food like all other breeds do.
Sled dogs are not usually the angry guard dog archetype shown here. Most are quite friendly in real life.
Dogs are really good swimmers in real life, so the sled dogs should not have drowned when they are swallowed by the frozen lake.
Wolf packs have no such thing as an "alpha" in the way they are portrayed in this special. Instead, they are close-knit familial groups consisting of parents and several generations of that breeding pair's offspring, generally have very little internal conflict, and do not operate on a dominance-based system any animal could "take over" by force. For that matter, while dogs do form complicated social dynamics, they never operate in the clear-cut pecking order that is portrayed in this special.
During the dogfight scene, both Snoopy and the Alpha Male husky are biting and clawing at each other. They both should have been showing serious, visible injuries, but there is no blood seen and they both appear to be unharmed.
Snoopy puts chocolate syrup on his ice cream sundae. Chocolate makes normal dogs sick, but as Charlie Brown has repeatedly remarked in various cartoons, Snoopy is not a normal dog.
The sled dog at the third harness part on the left side appears to be orange at the bottom and brown at the top. When the sled dogs get angry after Snoopy howls like a wolf, the latter sled dog's fur turns beige while snarling at him. In the next two shots, while the sled dogs are falling asleep, his fur turns back to orange, but when Snoopy sneaks up to the Alpha Male Husky while he is trying to stay warm during his sleep, the other sled dog's fur turns back to beige.
Snoopy forgets to put the ice cream that he used for making his ice cream sundae back in the freezer, leaving it to melt all night.
When the sled dogs in Snoopy's nightmare eat outside the root beer saloon, The sound of them eating starts before they are even eating.