Simple request, "Do me a favor, let's run the original code so I can see the original behavior."
in reply to Looking For The Obvious - Debugging Perl
If the reply is "sure" and they do, you can run a diff on the files, as well as possibly trust the information this person gives you.
If the answer is "no <insert reason or personality defect here>", don full bomb squad protective gear, activate all sensing devices, prepare for battle on all fronts. This person is either hiding something (won't run original code) or is too <place insulting reference to sub normal intelegence here> to have made a back up of the original code. Either case requires extreme caution as you are going to be held responsible until the code works.
No Fear, No Brains. If we didn't pay attention to some of our fears, we would do stupid or possibly deadly things like smoke, talk on cellphones in traffic, drive vehicles while drunk and so on.