Pass out a mushroom, a piece of white paper, and a cup to each person.
Break off the mushroom stem so that the cap can be laid down fairly flat.
Lay the mushroom gill-side-down on the piece of paper.
Carefully cover the mushroom cap with the open end of the glass or bowl.
Let the mushroom sit for at least an hour, preferably overnight.
GENTLY lift the glass or bowl from the mushroom and VERY GENTLY lift the mushroom cap from the paper. You should see a beautiful radial design.
If you want to save the design, spray the paper with clear acrylic.