The case sensitivity issue is simple, use "i" with your s/ to make the operation "case insensitive":

$line =~ s/(\S+)/$dict{$1} || $1/egi;
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The problem with "man-kind" is this: \S includes "-", but \w does not!

my ( $key, $val ) = /^(\d+)\s+(\w+)/;
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If you print the value of your keys, I think you will find #4 is just "man".

By the way, the "key" to a hash is it's name. The "value" of a hash is the data it contains. Altho it will not affect the functioning of your code, you have this nomenclature backward in the code which creates the dictionary.