Mix cherry gelatin dessert mix with ½ cup boiling hot water in a 1 quart sized measuring cup or pitcher with a spout.
Stir for about 2 minutes until the gelatin is fully dissolved.
Add 2 ½ cups cola slowly to the gelatin mixture. Mixture will foam up quite a bit.
Stir until well incorporated.
Add rum to cola and gelatin mixture.
Mix well to fully combine. There will still be foam on top of the mixture.
Arrange 2 ounce portion cups in a baking pan.
Pour the gelatin mixture into 2 ounce portion cups.
Place the lids on the portion cups if desired. (I did this, so I could stack the shots on top of each other in the pan while they chilled in the fridge.)
Place in the refrigerator for 4 hours to fully congeal. (I would make these the day before if I wanted them for a party to ensure they were fully set.)