Wow, I didn't think anyone would actually respond to this. @JavaFan Best. Response. Ever.

I tried running

use Data::Dumper;
$Data::Dumper::Useqq = 1;
print Dumper($str);
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from the command line with

print Dumper("6 1/2")
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but what's interesting is that every time I would copy/paste "6 1/2" from the Most Holiest of Editors Emacs, it would come out as "1/26" on the command line. Then Dumper would say it just contains "1/26", which is not helpful.

So I gave up on that and put the code right in my script. The results from that were much more interesting:

$VAR1 = "6\2401\\/2";
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So, it looks like I have a \240 running a muck in my data. Googling tells me this should actually show up as ð but The Most Righteous of Editors was displaying my data in iso-latin-1-unix encoding, as opposed to straight-up UTF-8.

Thanks so much, monks.