Pour ⅓ cup of water into each Styrofoam cup.
Add 1 tablespoon of vinegar and 12–15 drops of food coloring to each cup, stirring well.
Mix in ½ cup of popcorn kernels so they’re fully coated.
Let the kernels sit for 5–6 hours, then spread them out on a paper towel–lined baking sheet to dry overnight.
Draw a pumpkin outline (or another fall design) on white paper.
Apply glue to small sections of the outline.
Press the colored kernels onto the glue to fill in the design.
Allow the mosaic to dry completely before displaying.