Step #1: Determine which side you want to carve. If necessary, cut a small slice off the opposite side so the melon sets flat.
Step #2: Using a sharp knife, carefully peel most of the green outer layer away from the watermelon, exposing the white layer below. Cut away most of the white layer in a few areas to expose a light pinkish color.
Step #3: Using the brain picture as a guide, score lines on the melon with a toothpick.
Step #4: With a sharp paring knife, carefully carve the scored lines, cutting away the white layer and exposing the melon's flesh.
Step #5: Serve immediately.
For added grossness!
At serving time after your guests have had a chance to appreciate your master carving skills, begin "dissecting" the brain by cutting through the carved layer and exposing the "fleshy goodness" inside. Dig in!