The really foolish part about all this bloodletting is that people always seem to want to slash their palms. They grab knives, slide their hands down swords, and slice n dice their palms to bits.
This is a terrible idea.
Look, if you want to cut yourself in an obvious way you should *clearly* make a slash on the back of your arm just above the wrist. Easy to bandage, easy to keep an eye on. When you slash your palm though you have a bandage around your hand. This is a disaster from a utility standpoint. You are clumsy, you risk opening the wound if you use your hand for anything, the bandage will be hard to apply properly and will easily come off. The back of the forearm doesn't have any of these penalties!
Plus the back of the forearm has little in the way of nerves so it won't hurt nearly as much.
So the next time a wizened old warlock tells you that your blood has the power to do some big exciting ritual blah blah blah do yourself a favour and don't cut your palm. When the big powerful leader demands a show of loyalty and for some reason they want that to include blood, keep in mind that you need your hands for things and the big power leader wants you to be effective. Back of the forearm, that is the ticket.
You are welcome.