As much fun as answering this kind of questions is, I'd like to note that you shouldn't rely an interview just on technical issues. You shouldn't start by asking Perl questions and choose the candidate with more knowledge (and that is also because the guy might be just nervous).

Other things are also important... can you rely on the guy to spend some time with people who need his help? can you rely on him/her working harder when the deadline approaches? Will he/she be a nice person to have around? :-)

All those things count :-)