Let's say that you need some blood (for whatever reason), and you don't have a needle. What's a good way to get blood?

You can slice your finger with a knife, but that seems inconvenient to me since it's your finger and it'll probably be an inconvenience if you're doing any sort of handy work. Is there another safe area to cut, like your forearm?
In case anyone is wondering, I'm not doing any spells or incantations.