Laughing Gas; available from the
dentist,
Whip-It canisters, and
Dead shows, as well as in
tanks from
medical and
restaurant supply stores. (There are also even more
dangerous forms of N
2O: auto-grade and homemade).
A lungful of the gas produces about thirty seconds of auditory hallucinations (likened to quickly covering and uncovering one's ears), communion with the cosmic yin-yang, and possible minor brain damage. Studies of addicted dentists and emergency room walk-ins document that larger quantities and long-term use can cause paralysis and dementia; everyday risks include frost-bite (from the release of the pressurized gas) and asphyxiation.
Recreational use usually involves the aforementioned Whip-Its used for dispensing whipped cream and sold in many grocery stores. Other devices include crackers—metal or plastic devices sold in head shops and specifically made for releasing the Whip-It into a balloon—and charging bottles similar to the CO2 type used for seltzer mentioned by moscow above.