Let your brownies cool completely, then cut into 12 rectangles.
Make the icing by whisking together the powdered sugar and milk in a small bowl. Transfer the icing to a pastry bag or a ziploc bag and make a small cut at the tip of the bag where the icing can drizzle out.
Drizzle icing across brownies in a zig-zag pattern, then place two eyes on each brownie.
Leave icing to harden for about 10 minutes, then serve.