In a saucepan, bring the cream, sugar and lemon extract to a simmer. Slowly sprinkle the calcium lactate into the pan and mix with a hand blender. Chill.
Meanwhile prepare the molds (I use a small flexi-mold, but any mold that is able to be flexible will do) with a dot of melted chocolate to resemble a pupil, and place in the refrigerator to set. Then brush the blue cocoa butter to resemble the iris, and pipe in the jelly to resemble bloody veins.
Once the cream mixture is cold, whip to a soft peak using a hand mixer. Pipe into the prepared molds and freeze until set.
Unmold the eyeballs and leave them soaking in the Alginate Solution for about 2 minutes. Then rinse with cold water and store in the fridge until you are ready to serve.
Place the eyeballs in a dish (2 each is appropriately scary) and top with the lime soda. I find that a clear soda without color gives the eyeballs a better look and flavor.
Sprinkle the sodium alginate into the water and, using a hand blender, mix the solution until there is no more visible powder left. This takes a couple of minutes. Chill the solution until you are ready to use it.