
Doc Brown, a character from the Back to the Future trilogy, is a time traveling scientist known for his eccentric personality and absent-mindedness. A component of this strip’s punch-line is his most well known catch phrase: “Great Scott!”
This comic is humorous because the child has dressed up as the Doc Brown character and attempted trick-or-treating on October 30th - one day before Halloween. This is just the kind mistake, and reaction to said mistake, that could be expected from “Doc.”