It’s laughing gas. Nitrous oxide. Usually in small cylinders used for a brief high. Gives you a headache if done repeatedly.
At the restaurant, we had a giant cylinder used for making whipped cream.
Thank you! It does not sound like a very smart thing to do. My mom told my brother and I about college parties she’d gone to where little vials of amyl nitrate-”poppers”-were offered along with the beer and other alcohol. That didn’t sound like something I’d want to do, either...