Dave and friends are packing soggy straw into cardboard boxes. With each handful of wet straw, they sprinkle a handful of mushroom spores. When full, the boxes get stuffed into a closet for a month.
Then the boxes come out into the light and the fungus starts to grow fruiting bodies (edible and tasty).
After a month in the closet, the fungus ate through this box and is already starting to fruit.