That is the main problem! You cannot practice unless you know a pig farmer who will let you stick a couple of rosy piggies per week at a good price! But I doubt he will let you even if you are his best friend

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In all seriousness, if you want to do spear-only hunting, the best practice is to go jogging a lot and stop smoking! For the rest, just keep your blade razorsharp, and rely on your wildest instincts : the final act is easy, you will know what to do without thinking!