Lesson learned during my Handmade Film workshop...
Why you should not use a knife to open a cartridge of Super 8 film:
And that's after one week of healing, so just imagine how nasty it was at first!

Okay, maybe most people would not try to open a Super 8 cartridge with a knife, but who knew you could do that much damage with a butter knife?! Anyway, I've learned that it's better to pull the 50' of film out of the cartridge than to try to actually open the cartridge. (And if you didn't shoot the entire roll, just burn off the end anyway so you can pull it out easily.)
As for the workshop itself, I'll talk about that as soon as I have transferred my hand processed film to digital (for some reason, the DVD that was supposed to have my transfer on it was completely blank... *sigh*).