You can use B::Deparse to unravel it (or any other obfuscation):

% perl -MO=Deparse obfu.pl
'' =~ m[(?{print "plus three five three eight six two five five one fi
+ve
four one stop congratulations paisano stop email conor with subject no
+de
one secure stop",$/})];
obfu.pl syntax OK
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Update:  as ++mtve shows with a clever example, it B::Deparse doesn't necessarily tell you much...