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sub tokenize_msg_w_oneregex {
    my ($msg) = @_;
...

    return keys %words;
}

Benchmark: timing 10000 iterations of Lists, One Regex, Strings...
     Lists:  4 wallclock secs ( 4.15 usr +  0.00 sys =  4.15 CPU) @ 24
+09.64/s (n=10000)
...
Lists     2410/s        --      -14%      -44%
One Regex 2809/s       17%        --      -35%
Strings   4292/s       78%       53%        --