Peel your radishes until they are a round shape, trying to leave streaks of the outer red skin here and there so that it resembles veins. Then scoop out a small round area of the radish with the top of your potato peeler. Slice your olive in half, or until if fits snugly into your radish hole. Put your eyeballs into an ice cube tray and carefully fill with water. Freeze.
Tips: Your olives may start to fall out when they are in the water. You can prevent this by sticking a toothpick in straight through the olive and slightly into the radish. Halfway through the freezing process, carefully remove the pick.
Another tip is to use a large ice cube form. The 2 x 2 size works well for this project. But if your radishes are on the smaller size, a regular sized ice cube tray will do.