A nang is the Australian slang term for a co2 (nitrous oxide, laughing gas) canister, intended for whipping cream but also used as a recreational drug.
They're also known as bulbs, whippits (reference to whipping cream) or cream chargers.
The nang is "cracked" with a nangerator; a soda syphon, commercial cream whipper or purpose built unit made to depressurize the gas for inhalation. The name comes from an auditory hallucination some users get while effected. A heavy user may be dubbed a "nangasaurus rex"
Nitrous Oxide (laughing gas - used as anaesthetic in dentistry) filled little gas cylinders normally used in a
whipped cream syphon ('Nang machine') in cafes etc, but inhaled slowly directly into the mouth or via a filled balloon. Gives a detachment high for around one minute. Term nang thought to come from Western Australia and from the sound distortion you have while affected. It's legal to buy in all states in Australia. Usually accompanies other drugs such as ecstacy pills and acid. Purchased in box of ten from delis, servos and supermarkets.