Start by pouring the fruit juice or flavored water into a saucepan and warming it over medium heat until it's hot but not boiling.
sprinkle the unflavored gelatin powder evenly over the warm liquid, then whisk continuously until the gelatin fully dissolves and the mixture is smooth.
Stir in the sugar if using, ensuring it dissolves completely and the mixture remains glossy and slightly thickened.
Divide the gelatin mixture into separate bowls if you plan to use different colors, and add a few drops of food coloring to each bowl, stirring gently until the colors are vibrant.
Pour a thin layer of the colored gelatin into each cavity of your brain-shaped mold, filling just halfway to create depth.
Add small pieces of fruit slices or candies into the partially filled mold, arranging them to resemble internal features of a brain.
Gently pour the remaining gelatin mixture over the fruit, filling the mold to the top without disturbing the fruit placement.
Place the mold in the refrigerator and chill for at least 4 hours or until the gelatin is firm and jiggles nicely.
Once set, gently unmold the gelatin by running warm water over the outside of the mold for a few seconds, then carefully invert onto a serving plate.
Observe the gelatin's translucent, squishy appearance, with colorful internal details peeking through, perfect for a spooky yet edible decoration.
Slice or serve the brain-shaped gelatin as desired, letting it wobble invitingly and ready to delight your spooky guests.
