The Murderhorn is stated to be over four miles (21,120 feet) in height. This is taller than Mount McKinley, which is the biggest mountain in the United States. This is likely an intentional joke continuing the running gag of Springfield having impossible geography.
In the flashback, the can of flapjacks seems to be rested on McAllister's foot, yet it is drawn totally flat as if it is on the ground.
When Grampa's teeth fall out of his mouth, they perfectly fit McAllister's bite wound, revealing it was Grampa that tried to take a bite out of him, just as McAllister had recorded in his journal. However, Grampa was a young man at the time and would have had his regular teeth, not dentures; therefore they should not perfectly fit the wound like this.