I did play with CO2 a lot when I was a kid, though. I used to buy the little canisters that serve some purpose or other for home brewing, and hammer nails through the ends so they went off like rockets and skittered all over the yard. There was a lot of visible gas, but maybe the expansion of the CO2 made it cold and so I was seeing condensing water? Also I played with the soda stream a lot, I think CO2 has a distinctive taste.
I enjoy referencing the oxygenation event extinction too. Goddam cyanobacteria, messing up the greenhouse for us archaea with their oxygen pollution.