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The best option is to buy these. We tried to make them during HAMLET '17 and it didn't work very well - we ended up just having the actors drink the blood from a cup. We tried buying empty capsules and filling them with edible blood we made ourselves, but the capsules dissolved way too quickly to be usable since the blood inside was liquid not powder.
Costume stores/Garment District sells crappy ones that you have to spend a minute chewing to get the powder liquid enough to be realistic. This involves a lot of saliva/time before the pack is spat out.
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