I have no idea where to start parsing

You may not know it, but it's very easy to tap into perl's own parser, and find out what it thinks of a given piece of code:

% perl -MO=Deparse chester
chester syntax OK
$+ + s/\\\s q\\+//s
    + s/$/$$/s / s///s
    . s[{q`!^/s.`^q\s][. s]s
    . s/\d*/do { 'JAPH' }/es + 'es)/$'
    + s/$_\$/$_$_/s
    + s///s
    + print($_);
[download]

(whitespace added for clarity).

Once it's been through the wringer it becomes clear what is happening (well, to me at least). As it turns out, it looked like chester threw a couple of diversions in the mix.

It used to be that a particularly clever obfu will cause B::Deparse to crash, which would prevent such casual analysis. As a result, for better or worse, B::Deparse has lots more smarts these days and it's just about impossible to trip it up. Much kudos is earnt by managing to do so.