(For the non-alcoholic, dry ice-free version, see the color-changing sports drink)
Step 1: Ingredients
Gin (or vodka, for a vodka martini) ~ Vermouth ~ Dry Ice ~ Baking Soda ~ Red Cabbage
Step 2: Red #$@%! Cabbage?
To get the indicator, chop up a cabbage leaf, put it in a bowl with some water, and microwave until it's boiling (or just add boiling water and allow to steep). A purple pigment will stain the water.
Step 3: Build
Step 4: Present
(that's not me saying "wow, that's wicked" by the way. This drink was mostly made as a way of keeping three small children entertained while their mother was out Christmas shopping. They liked the look of the cocktail, but thought the mocktail version was "really disgusting". I did warn them that it was just salty, cabbage-flavoured water...)It should go without saying, but wait for the dry ice to disappear before trying to drink the cocktail. You do NOT want to swallow any dry ice!
Step 5: Taste
I didn't initially regard this drink as spooky in any way, so was surprised to see it appear on various "Creepy Halloween Foods" lists (dabbled, neatorama, mentalfloss, etc). The lists were great and well worth checking out (they included some really effective eyeball recipes - see here for my version).