This is a fine example of one quotation standing on the shoulders
of another - a proverb, in this case. 'An eye for an eye, a
tooth for a tooth' is a traditional expression of revenge thinking
that dates back to biblical times. And just as some quotations
take a literal statement and turn it into a metaphor, here we
have a metaphotrical statement which is turned into something
literal. It is clever rhetoric, and the identity of the author
gives it added point.