Wash and dry the exterior of the watermelon thoroughly.

Cut a small, flat slice off the bottom of the watermelon so it sits securely on a cutting board without rolling.

Using a dry-erase marker, draw a large wedge shape for the mouth on the front end of the watermelon.

Use a chef's knife to cut out the wedge. Save the rind from this piece to make the dorsal fin.

Using a melon baller or spoon, scoop out the flesh from the mouth and hollow out the interior. Save the flesh in a bowl.

With a paring knife, peel back a 1/2-inch border of green skin around the mouth opening to expose the white rind. Carve jagged triangles into this white rind to create teeth.

Cut a triangle shape out of the reserved rind wedge. Attach this dorsal fin to the back of the shark using toothpicks.

Carve two small divots above the mouth and insert a blueberry into each for the eyes, securing with broken toothpicks if needed.

Cut the scooped watermelon flesh into bite-sized cubes and fill the hollowed-out shark, letting the fruit spill out of the mouth.