Final answer:
Text excerpts reveal that the figures Mac and Dennis encountered exhibit unnatural movements, disturbing appearances, and disturbed behavior, all of which align with typical zombie traits and suggest they were not completely human.
Step-by-step explanation:
The evidence from the story that supports the idea the people Mac and Dennis saw were not "completely human" can be found in the provided text excerpts. One passage describes an awkward, shambling gait, and figures behaving in a manner that did not seem natural, which suggests unnatural movements. Another mentions a figure with a face that lacked a lower jaw, exhibiting a grotesque appearance that is certainly not characteristic of a human being, implying a disturbing appearance. Lastly, characters behaving with a lack of coordination or purpose, such as crawling or dragging themselves in unnatural ways, support the idea of disturbed behavior. These descriptions are consistent with typical zombie characteristics in literature and popular culture, which often include unnatural movements, a horrifying appearance, and confused or purposeless behavior.