Hacksaw, slack-jawed, like they short a chromosome
People that lack chromosomes often end up with physical and mental deformities such as “slack-jaws”. This is a continuation of the evolutionary talk of the previous two lines.
“Hacksaw” refers to the 1980s professional wrestler, Hacksaw Jim Duggon, who played the role of a buffonish redneck. So he was something of a “slack-jawed” yokel.
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