I use a razor. The only thing to be careful is that you don't puncture any of the zoas. Most zoas don't contain any paly toxin, but some do, and if you are allergic to it, it's a big deal. Always better to stay on the safe side.
It's also important to note that you will start to feel sick pretty much immediately if you inhale it (allergic or not). Just lie down and most of the time it will go away in 10-20 minutes. If it doesn't or you have issues breathing, get to the hospital.