Step 1: Thoroughly wash and dry the apples, removing any wax by dipping them briefly in boiling water and scrubbing with a clean cloth. Insert a wooden skewer into the stem end of each apple.
Step 2: In a medium saucepan, combine the sugar, water, and corn syrup. Stir over medium heat until the sugar dissolves.
Step 3: Clip a candy thermometer to the side of the pan and bring the mixture to a boil. Continue cooking without stirring until it reaches 300°F to 310°F (the hard crack stage).
Step 4: Remove from heat and stir in the vanilla and red gel food coloring until the color is uniform and the bubbles have mostly subsided.
Step 5: Tilt the pan and dip each apple, swirling it to coat it completely. Lift the apple and let the excess syrup drip off before placing it on a silicone mat or parchment paper.
Step 6: While the candy is still slightly tacky, carefully press the candy eyeballs into the surface of the bloody eyeball candy apples to create a staring effect.
Step 7: Allow the apples to cool and harden completely at room temperature for at least 30 minutes before serving.