the 'what else' is only limited by your time, energy, and interest. what other heuristics could/should you use to avoid having to do the md5sum? at what point would those heuristics become more harmful than helpful? is there some much more clever way to prove that the files are identical or different? etc.

12.rb takes 0m0.204s on my /usr/include. 11.pl takes 0m3.066s. why? do you know? i'm kind of interested. maybe i'll check that out. there is always more to whatever you're looking at. you just stop when you lose interest or lack energy.